首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2302篇
  免费   149篇
  国内免费   34篇
耳鼻咽喉   30篇
儿科学   86篇
妇产科学   38篇
基础医学   255篇
口腔科学   65篇
临床医学   230篇
内科学   519篇
皮肤病学   120篇
神经病学   141篇
特种医学   237篇
外科学   342篇
综合类   56篇
一般理论   8篇
预防医学   161篇
眼科学   28篇
药学   89篇
中国医学   4篇
肿瘤学   76篇
  2021年   15篇
  2019年   17篇
  2018年   16篇
  2017年   22篇
  2016年   30篇
  2015年   40篇
  2014年   42篇
  2013年   87篇
  2012年   46篇
  2011年   63篇
  2010年   78篇
  2009年   75篇
  2008年   49篇
  2007年   70篇
  2006年   73篇
  2005年   70篇
  2004年   61篇
  2003年   62篇
  2002年   54篇
  2001年   70篇
  2000年   57篇
  1999年   49篇
  1998年   97篇
  1997年   88篇
  1996年   93篇
  1995年   64篇
  1994年   69篇
  1993年   57篇
  1992年   51篇
  1991年   35篇
  1990年   49篇
  1989年   75篇
  1988年   61篇
  1987年   54篇
  1986年   43篇
  1985年   42篇
  1984年   34篇
  1983年   22篇
  1982年   26篇
  1981年   27篇
  1980年   24篇
  1979年   32篇
  1978年   26篇
  1977年   27篇
  1976年   19篇
  1975年   17篇
  1974年   13篇
  1973年   22篇
  1972年   17篇
  1969年   14篇
排序方式: 共有2485条查询结果,搜索用时 31 毫秒
71.
Body size plays an important role in pinniped ecology and life history. However, body size data is often absent for historical, archaeological, and fossil specimens. To estimate the body size of pinnipeds (seals, sea lions, and walruses) for today and the past, we used 14 commonly preserved cranial measurements to develop sets of single variable and multivariate predictive equations for pinniped body mass and total length. Principal components analysis (PCA) was used to test whether separate family specific regressions were more appropriate than single predictive equations for Pinnipedia. The influence of phylogeny was tested with phylogenetic independent contrasts (PIC). The accuracy of these regressions was then assessed using a combination of coefficient of determination, percent prediction error, and standard error of estimation. Three different methods of multivariate analysis were examined: bidirectional stepwise model selection using Akaike information criteria; all‐subsets model selection using Bayesian information criteria (BIC); and partial least squares regression. The PCA showed clear discrimination between Otariidae (fur seals and sea lions) and Phocidae (earless seals) for the 14 measurements, indicating the need for family‐specific regression equations. The PIC analysis found that phylogeny had a minor influence on relationship between morphological variables and body size. The regressions for total length were more accurate than those for body mass, and equations specific to Otariidae were more accurate than those for Phocidae. Of the three multivariate methods, the all‐subsets approach required the fewest number of variables to estimate body size accurately. We then used the single variable predictive equations and the all‐subsets approach to estimate the body size of two recently extinct pinniped taxa, the Caribbean monk seal (Monachus tropicalis) and the Japanese sea lion (Zalophus japonicus). Body size estimates using single variable regressions generally under or over‐estimated body size; however, the all‐subset regression produced body size estimates that were close to historically recorded body length for these two species. This indicates that the all‐subset regression equations developed in this study can estimate body size accurately.  相似文献   
72.
The eyes of rhesus monkeys were exposed to argon (514.5 nm) and ruby (694.3 nm) laser irradiation using various retinal image diameters which were estimated by microphotometric techniques. The experimental design for both wavelengths produced image diameters of 40μ to 50μ for the “minimal” case and approximately 500μ to 1,000μ for the larger irradiance series employed. Extramacular retinal exposure sites were examined by ophthalmoscopic and histopathological techniques. Flat preparations of the pigmented epithelium and sensory layers of the retina were utilized in the confirmation of damage at low power levels. All data were statistically analyzed to establish trends, and results were compared for the wavelengths employed. Results indicate that retinal damage is primarily dependent on energy distribution as a function of image diameter and exposure duration.  相似文献   
73.
74.
75.
Du  X; Beutler  L; Ruan  C; Castaldi  PA; Berndt  MC 《Blood》1987,69(5):1524-1527
Two new murine monoclonal antibodies, AK 1 and SZ 1, reactive with the human platelet glycoprotein (GP) Ib-IX complex have been produced by the hybridoma technique. Both AK 1 and SZ 1 immunoprecipitated the GP Ib-IX complex from Triton X-100-solubilized, periodate-labeled platelets. With trypsinized, labeled platelets, AK 1, SZ 1, and FMC 25 (epitope on GP IX) immunoprecipitated a membrane-bound proteolytic fragment of the GP Ib-IX complex consisting of GP IX and an congruent to 25,000 mol wt remnant of the alpha-chain of GP lb disulfide-linked to the beta-subunit. Unexpectedly, although AK 1 and SZ 1 immunoprecipitated purified GP Ib-IX complex, neither antibody immunoprecipitated the individual components of this complex, GP Ib or GP IX. When GP Ib and GP IX were recombined, however, AK 1 and SZ 1 again immunoprecipitated the reformed complex, strongly suggesting that both antibodies were recognizing an epitope present only on the intact complex. Cross-blocking studies indicated that AK 1 and SZ 1 recognized a very similar or identical epitope that was proximal to the epitope for FMC 25. Both AK 1 and SZ 1 bound to a similar number of binding sites (congruent to 25,000) on intact platelets as monoclonal antibodies directed against either GP lb or GP IX. The combined data suggests that GP lb and GP IX are fully complexed in the intact platelet membrane.  相似文献   
76.
The myeloproliferative syndrome induced by the myeloproliferative sarcoma virus (MPSV) in DBA/2 mice stimulates the proliferation of pluripotent hemopoietic stem cells (HSC) and of progenitors committed toward granulomacrophagic and erythroid cell lines. This stimulation may result from a direct effect of the MPSV on HSC or from an indirect effect via locally secreted factors. Normal isogenic bone marrow cells were incubated in the mixed colony-forming unit system in semisolid medium supplemented with conditioned media obtained after incubating neoplastic spleen cells for 3 days at 37 degrees C. These spleen conditioned media contain an activity that is physically separable from MPSV by ultracentrifugation and which, in the presence of a very low quantity of erythropoietin, can induce in vitro the proliferation and differentiation of pluripotent HSC, detected by this Mix-CFU technique. We termed this activity mixed-colonies promoting activity (MPA). These results suggest that the hyperplasia of the nonlymphoid hematopoietic system in the neoplastic spleen results from an indirect effect of the MPSV on pluripotent HSC via locally secreted factors.  相似文献   
77.
A previous study revealed that the difference in susceptibility to atherosclerotic lesions between inbred mouse strains SM/J and NZB/BlNJ was determined by one major locus (Ath8). In this study a (SM/J x NZB/BlNJ) F(1) x SM/J backcross localized Ath8 by quantitative trait locus mapping to chromosome 4 with a suggestive LOD score of 2.7. This quantitative trait locus (QTL) was confirmed using an (SM/J x NZB/BlNJ) intercross; Ath8 mapped to a 23cM region with a significant LOD score of 3.6. The genes for toll-like receptor 4 (T1r4), arachidonic acid epoxygenase (Cyp2j5), and angiopoietin-like protein 3 (Angptl3) map to this region. These candidate genes were analyzed for expression and sequence differences in the mouse and for associations with cardiovascular traits in human. Sequence analysis of Angptl3 shows a base pair substitution in SM, the susceptible strain, giving rise to an amino acid change in the fibrinogen homology domain of the protein. We found a significant association between ANGPTL3 and atherosclerotic lesions (P < 0.05) in human. These results suggest that Angptl3 is involved in atherosclerosis susceptibility in both mouse and human.  相似文献   
78.

Background

Early in medical education, physicians must develop competencies needed for tobacco dependence treatment.

Objective

To assess the effect of a multi-modal tobacco dependence treatment curriculum on medical students’ counseling skills.

Design

A group-randomized controlled trial (2010–2014) included ten U.S. medical schools that were randomized to receive either multi-modal tobacco treatment education (MME) or traditional tobacco treatment education (TE).

Setting/Participants

Students from the classes of 2012 and 2014 at ten medical schools participated. Students from the class of 2012 (N?=?1345) completed objective structured clinical examinations (OSCEs), and 50 % (N?=?660) were randomly selected for pre-intervention evaluation. A total of 72.9 % of eligible students (N?=?1096) from the class of 2014 completed an OSCE and 69.7 % (N?=?1047) completed pre and post surveys.

Interventions

The MME included a Web-based course, a role-play classroom demonstration, and a clerkship booster session. Clerkship preceptors in MME schools participated in an academic detailing module and were encouraged to be role models for third-year students.

Measurements

The primary outcome was student tobacco treatment skills using the 5As measured by an objective structured clinical examination (OSCE) scored on a 33-item behavior checklist. Secondary outcomes were student self-reported skills for performing 5As and pharmacotherapy counseling.

Results

Although the difference was not statistically significant, MME students completed more tobacco counseling behaviors on the OSCE checklist (mean 8.7 [SE 0.6] vs. mean?8.0 [SE 0.6], p?=?0.52) than TE students. Several of the individual Assist and Arrange items were significantly more likely to have been completed by MME students, including suggesting behavioral strategies (11.8 % vs. 4.5 %, p?<?0.001) and providing information regarding quitline (21.0 % vs. 3.8 %, p?<?0.001). MME students reported higher self-efficacy for Assist, Arrange, and Pharmacotherapy counseling items (ps?≤0.05).

Limitations

Inclusion of only ten schools limits generalizability.

Conclusions

Subsequent interventions should incorporate lessons learned from this first randomized controlled trial of a multi-modal longitudinal tobacco treatment curriculum in multiple U.S. medical schools.NIH Trial Registry Number: NCT01905618
  相似文献   
79.
Allogeneic bone marrow transplantation (BMT) for advanced acute leukemia is associated with a high risk of relapse. It is postulated that interleukin-2 (IL-2) administered after BMT might induce or amplify a graft-versus-leukemia effect and thereby reduce the relapse rate. To identify an IL-2 regimen for testing this hypothesis, a phase I trial of IL-2 (Roche) was performed in children in complete remission (CR) without active graft-versus-host disease (GVHD) off immunosuppressive agents after unmodified allogeneic matched-sibling BMT for acute leukemia beyond first remission. Beginning a median of 68 days after BMT, 17 patients received escalating doses of induction IL-2 (0.9, 3.0, or 6.0 x 10(6) IU/m2/d representing levels I, II, and III) for 5 days by continuous intravenous infusion (CIV). After 6 days of rest, they received maintenance IL-2 (0.9 x 10(6) IU/m2/d) for 10 days by CIV infusion. Levels I and II were well-tolerated, but, of 6 patients at level III, 1 developed pulmonary infiltrates, 1 developed hypotension (both resolved), and 1 died of bacterial sepsis and acute respiratory distress syndrome. Grade II acute GVHD developed in 1 patient at level I and 1 at level III. The maximum tolerated dose of induction IL-2 was level II. IL-2 induced lymphocytosis, with an increase in CD56+ and CD8+ cells. Ten patients remain in CR at 5+ to 67+ months. Thus, a regimen of IL-2 has been identified that did not induce a high incidence of acute GVHD when administered to children after unmodified allogeneic BMT. Its clinical activity will be assessed in a phase II trial.  相似文献   
80.
We employed the research-to-practice consensus workshop (RTP; workshops held in New York City and Tompkins County, New York, in 2013) model to merge researcher and practitioner views of translational research priorities in palliative care. In the RTP approach, a diverse group of frontline providers generates a research agenda for palliative care in collaboration with researchers. We have presented the major workshop recommendations and contrasted the practice-based research priorities with those of previous consensus efforts. We uncovered notable differences and found that the RTP model can produce unique insights into research priorities. Integrating practitioner-identified needs into research priorities for palliative care can contribute to addressing palliative care more effectively as a public health issue.Over the past 2 decades, palliative care has become established as a promising approach for addressing the needs of individuals with life-threatening illnesses from a holistic, interdisciplinary perspective. For this project, we defined palliative care as an approach that improves the quality of life of patients and families facing the problems encountered in life-threatening illness by preventing and relieving suffering. Core components of palliative care include providing relief from pain and other distressing symptoms, affirming dying as a normal process, integrating psychological and spiritual aspects of care, enhancing the quality of life of patients, and offering support systems to patients and their families to help them live as fully as possible until death occurs.Research suggests that palliative care results in positive patient outcomes, greater patient and family satisfaction, and significant cost savings.1,2 The American Public Health Association, the World Health Organization, and the Institute of Medicine3–6 have identified the development of a robust palliative care delivery system as a key public health issue because of the documented ability of palliative care to deliver effective and efficient patient- and symptom-focused care to a growing population in need.In its 2013 report the American Public Health Association specifically detailed the public health implications of palliative care, acknowledged the growing burden of advanced chronic illness and disease in older adults, and recommended key steps to address the problem. This policy statement called for federal, state, and local efforts to promote effective symptom management in populations with serious illness or at the end of life. Other recommended initiatives included the development of a palliative care workforce, educational programs to improve uptake and use of palliative and hospice care, and research funding to support the expansion of palliative care initiatives. Achieving these goals will require moving beyond traditional medical practices to include both policies and initiatives at the public health level.Despite the potential of palliative care to address the mental and physical health needs of individuals with advanced illness, significant knowledge gaps impede its reach and effectiveness. Reports from scientific bodies and consensus workshops have highlighted weaknesses in the literature and called for more research on palliative care and improved research methods.7–10 Thus, although both interest in and demand for palliative care are increasing, reviews of the knowledge base continue to lament the lack of research on many key issues.11,12Especially urgent is a research agenda that fits most closely with the needs of providers who deliver palliative care. The systematic engagement of community practitioners in a consensus process can lead to particularly useful and actionable recommendations for research,13–15 which are greatly needed at this stage in the development of the field. Therefore, to shed new light on research priorities in palliative care, we used a structured, participatory method designed to solicit practitioner input on research priorities: the research-to-practice consensus workshop (RTP) model.16We employed the RTP approach to identify knowledge gaps and types of studies that should be conducted to improve providers’ ability to deliver palliative care most effectively. This model harnesses practice wisdom by engaging clinicians, agency staff, and other practitioners with researchers in a process of articulating and refining research questions and research priorities that honors scientific expertise and practice wisdom.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号