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   9036篇
  免费   861篇
  国内免费   11篇
耳鼻咽喉   65篇
儿科学   263篇
妇产科学   198篇
基础医学   1128篇
口腔科学   151篇
临床医学   906篇
内科学   2108篇
皮肤病学   187篇
神经病学   734篇
特种医学   402篇
外科学   1000篇
综合类   285篇
一般理论   7篇
预防医学   1102篇
眼科学   125篇
药学   513篇
中国医学   4篇
肿瘤学   730篇
  2022年   62篇
  2021年   117篇
  2020年   83篇
  2019年   109篇
  2018年   151篇
  2017年   112篇
  2016年   113篇
  2015年   149篇
  2014年   202篇
  2013年   307篇
  2012年   409篇
  2011年   384篇
  2010年   272篇
  2009年   204篇
  2008年   356篇
  2007年   427篇
  2006年   429篇
  2005年   417篇
  2004年   397篇
  2003年   350篇
  2002年   302篇
  2001年   303篇
  2000年   301篇
  1999年   237篇
  1998年   129篇
  1997年   117篇
  1996年   96篇
  1995年   111篇
  1994年   83篇
  1993年   94篇
  1992年   235篇
  1991年   216篇
  1990年   203篇
  1989年   177篇
  1988年   206篇
  1987年   175篇
  1986年   171篇
  1985年   165篇
  1984年   105篇
  1983年   108篇
  1982年   75篇
  1981年   69篇
  1980年   59篇
  1979年   74篇
  1978年   88篇
  1976年   74篇
  1975年   73篇
  1973年   100篇
  1971年   64篇
  1970年   66篇
排序方式: 共有9908条查询结果,搜索用时 15 毫秒
81.
The numbers of women of childbearing age in the US with HIV and AIDS from heterosexual transmission continues to rise. Behavioral interventions remain the best means of preventing transmission of HIV. Program planners often implement interventions to promote behavioral change in a wide range of settings such as family planning or sexually transmitted disease clinics, drug treatment facilities, or medical facilities that serve high risk and HIV positive women. Women recruited in different types of settings, however, may differ with respect to their experience with, attitudes toward, and willingness to use condoms and contraception. Such differences should be considered when tailoring interventions to the populations being served. We examined the readiness to use condoms and contraception among 3784 women in four cities recruited in three different types of settings: community, facilities not targeted to HIV positive women and medical facilities for HIV positive populations. Readiness to use condoms or contraception was measured using The Transtheoretical Model of Change. Women reported being in different stages along the continuum of condom and contraceptive use in the three settings. A greater proportion of women in the HIV-facility, 45%, had used condoms consistently for the previous 6 months compared to women in the other two settings (12% and 11%). Similarly, variation across settings was seen for contemplation of consistent contraceptive use to prevent unintended pregnancies. The variability in the distribution of condom and contraceptive use across settings underscores the importance of assessing the readiness for the behavior change and designing interventions that meet the specific needs of the populations being served.  相似文献   
82.
The size frequency distributions of diffuse, primitive and classic beta-amyloid (Abeta) deposits were studied in single sections of cortical tissue from patients with Alzheimer's disease (AD) and Down's syndrome (DS) and compared with those predicted by the log-normal model. In a sample of brain regions, these size distributions were compared with those obtained by serial reconstruction through the tissue and the data used to adjust the size distributions obtained in single sections. The adjusted size distributions of the diffuse, primitive and classic deposits deviated significantly from a log-normal model in AD and DS, the greatest deviations from the model being observed in AD. More Abeta deposits were observed close to the mean and fewer in the larger size classes than predicted by the model. Hence, the growth of Abeta deposits in AD and DS does not strictly follow the log-normal model, deposits growing to within a more restricted size range than predicted. However, Abeta deposits grow to a larger size in DS compared with AD which may reflect differences in the mechanism of Abeta formation.  相似文献   
83.
The role of the clinical nurse specialist   总被引:6,自引:0,他引:6  
Despite the prevalence of clinical nurse specialists, research suggests that their role remains poorly understood (O'Hanlan and Gibbon 1996). In practice, they fulfil a number of important roles linked to developing practice. Here, the author critically examines the range of roles the clinical nurse specialist may undertake and how they influence patient care.  相似文献   
84.
Measurement tools used in the study of eccentric contraction-induced injury   总被引:14,自引:0,他引:14  
The objective of this review is to evaluate the measurement tools currently used in the study of eccentric contraction-induced muscle injury, with emphasis on their usefulness for quantifying the magnitude and duration of the injury and as indicators of muscle functional deficits. In studies in humans, it was concluded that measurements of maximal voluntary contraction torque and range of motion provide the best methods for quantifying muscle injury. Similarly, in animal studies, the in vitro measurement of electrically elicited force under isometric conditions was considered to be the best of the measurement tools currently in use. For future studies, more effort should be put into measuring other contractile parameters (e.g. force/torque-velocity and force/torque-length relationships maximal shortening velocity and fatigue susceptibility) that may reflect injury-induced functional impairments. The use of histology, ratings of soreness and the measurement of blood or bath levels of myofibre proteins should be discouraged for purposes of quantifying muscle injury and/or functional impairment.  相似文献   
85.
OBJECTIVE: One of the difficulties with lumboperitoneal (LP) shunts has been non-invasively ascertaining shunt function. It has been previously reported that in the presence of a functioning LP shunt the perimesencephalic cisterns become obliterated--the "absent cistern sign". In order to more rigorously test this association we performed a retrospective analysis of LP shunt patients at the Hospital for Sick Children, Toronto. METHODS: The CT scans of all patients undergoing LP shunting over a 17 year period were reviewed. The "absent cistern sign" and ventricular size were compared against the results of either an isotope shunt study or surgical findings performed within 2 days of the CT. RESULTS: There were 38 CT scans (27 patients) performed within 2 days of an isotope shunt study and 15 CT scans (14 patients) performed within 2 days of a surgical intervention. These results give the absent cistern sign a sensitivity of 75% and a specificity of 57% when compared to the shunt isotope findings and a sensitivity of 100% and a specificity of 50% when compared to the surgical findings. Over 30% of the CT scans showed ventriculomegaly in the presence of a functioning shunt and, conversely, nearly 45% of the CT scans had normal or small lateral ventricles in the presence of a malfunctioning shunt. CONCLUSIONS: The "absent cistern sign" appears to reliably rule out a completely blocked shunt, but is less reliable in detecting a normal or partially obstructed shunt. Ventricular size correlates poorly with LP shunt function.  相似文献   
86.
Simpson PB  Armstrong RC 《Glia》1999,26(1):22-35
We have examined the potential roles of intracellular Ca2+ regulation and of multiple cytoskeletal elements in control of the directed migration of cultured oligodendrocyte progenitor cells (OPs). OPs were found to migrate in response to platelet-derived growth factor (PDGF) or to a lesser extent to basic fibroblast growth factor (FGF) in a non-additive manner. This response was inhibited by chelation of intracellular Ca2+ by using BAPTA-AM. OP migration was not evoked by the neurotransmitter agonists phenylephrine or methacholine, which elevate OP Ca2+ levels. Inhibition of the MAP kinase pathway with PD 098059 did not affect OP migration to PDGF. Within growth cone-like leading edges of migratory OP processes, monomeric and filamentous actin were found to be colocalized with myosin and filamentous actin was prominent in filopodia extending beyond the leading edge. Tubulin was distributed throughout OP processes and cell bodies. Inhibition of actin or tubulin polymerization, by using cytochalasin B or nocodazole, respectively, altered OP morphology and markedly impaired migration. Inhibition of the myosin ATPase by BDM, which prevents force-generating actin/myosin interactions, greatly inhibited the chemotaxic response at concentrations that did not disrupt cell morphology. These results indicate that growth factors stimulate OP migration by activating pathways which include intracellular Ca2+ regulation, and characterize the distribution of multiple cytoskeletal elements involved in the generation of directed OP movement.  相似文献   
87.
Neutropenia is a common and often dose limiting side effect of some chemotherapy regimens. The aim of this study was to investigate the ability of an immunomodulator, glycosaminylmuramyl dipeptide (GMDP, CAS 78113-36-7, romurtide) to reduce chemotherapy induced neutropenia. BALB/c mice were treated with 200 mg kg-1 cyclophosphamide (CY) to induce a reversible neutropenia lasting approximately 6-7 days. There was no change in the duration or depth of neutropenia in mice treated with GMDP for 3 consecutive days (2.5 or 25 mg kg-1) starting the day after CY injection. In addition, at the doses used, the time of administration of GMDP relative to CY did not alter this response. However, a marked neutrophilia compared to controls was consistently observed in all cases. Neutrophil counts of up to 14 times the baseline value were measured 6-7 days after the induction of neutropenia. GMDP had no effect in the absence of CY. Less variation was seen in white cell counts of older non-SPF mice treated with CY. When the activity of GMDP (5 mg kg-1) was compared with G-CSF (granulocyte colony stimulating factor, 100 micrograms kg-1) in these animals, GMDP showed a consistent trend to reduce the length of neutropenia, however, under the conditions tested only G-CSF treatment resulted in a significant reduction in the duration of neutropenia. In the 12-week-old mice, the neutrophilia seen with both G-CSF and GMDP was much smaller than in the 8-week-old mice, and was not significantly different from that in control mice treated with CY alone.  相似文献   
88.
In the GUSTO-I ECG ischaemia monitoring substudy, 1067 patientsunderwent continuous ST segment monitoring, using vector-derived12-lead (406 patients), 12-lead (373 patients) and 3-lead Holter(288 patients) ECG recording systems. Simultaneous angiogramsat 90 or 180 min following thrombolytic therapy were performedas a part of the prospective study in 302 patients. Infarct vessel patency was established as TIMI perfusion grades2 or 3 and occlusion as TIMI perfusion grades 0 or 1. Coronaryartery patency was predicted from ST trends up to the time ofangiography. Predictive values at 90 and 180 min after the startof thrombolysis were 70% and 82% for patency and 58% and 64%for occlusion, respectively. In retrospect, accuracy appearedgreatest (79–100%) in patients with extensive ST segmentelevation (400 µV), if both speed of ST recovery and extentof ST segment: elevation were taken into account. Although thethree recording systems differed considerably in signal processing,no significant difference in accuracy was demonstrated amongthese systems. We conclude that continuous ECG monitoring may help select highrisk patients without apparent reperfusion who may benefit fromadditional reperfusion therapy. As ST recovery may occur earlyafter the start of thrombolytics and accuracy of the test isrelated to peak ST levels, the use of on-line ECG monitoringdevices on emergency wards and cardiac care units is recommended.(Eur Heart J 1996; 17: 689–698)  相似文献   
89.
Following a report of several relatives suffering from breast cancer, the occurrence of neoplasms in 3 generations of a large family was carefully checked. Members of one out of 8 branches were found to have a high incidence of breast cancer with 6 women affected, 4 of them under the age of 40. As well as early onset, these women presented other features typical of "breast cancer families": bilateral breast cancer, other second primary tumours, ovarian cancer in the daughter of one affected patient, and benign breast disease in the sister of another.  相似文献   
90.
The reader familiar with the borderline literature may see a correspondence between certain of our MPD/DD Rorschach results and typical borderline characteristics. Most notably, both groups reason and view others in unusual but not psychotic ways and demonstrate certain difficulties in affect integration. On the other hand, the MPD/DD group exhibits many attributes that contradict predictions one would make from a borderline perspective, and which support Kluft's assertion that the majority of these patients have a more complex and structured personality system. Rather than holding oversimplified attitudes, they are attuned to the subtleties of experience. Their generally introversive personality style reflects a capacity for internalization, for ideational organization of anxiety, for taking analytic distance from themselves, and for viewing and relating to others in a complex and empathetic fashion. To return to our metaphor of the explorer, we can conclude that the borderline personality concept gives us too broad and blurred a view of the MPD/DD terrain. It lacks the level of specificity needed to describe the test phenomena that appear on these MPD/DD Rorschachs. The special test instructions, behavior ratings of extra-test dissociative phenomena, and the posttest process questions enable us to see that although at gross level certain vulnerabilities resemble borderline characteristics, the processes underlying these phenomena are quite distinct. Moreover, unexpected areas of strength and maturity also exist. These findings suggest that we are not viewing a developmental arrest, but rather, are seeing the signs of what developmental psychologists call a "strange" development i.e., an atypical developmental pathway created by unusual interactions with the world. It may well be that much of the difficulty in establishing the validity of BPD test criteria has been due to the unwitting inclusion of DD patients within these studies. If so, the distinction between borderline and dissociative test characteristics will lead to more accurate and refined studies of both groups. The concept of PTSD has been a particularly useful dimension for elucidating MPD test phenomena. As we further investigate commonalities and differences within the MPD/DD continuum, it will be interesting to examine in what way the severity of these patients' PTSD relates to their personality characteristics, symptom patterns, and treatment response. The strength of psychological assessment has long been its ability to describe the organization of psychological processes to gain a detailed knowledge of the individual. As such, in the hands of well-trained clinicians, psychological assessment has been one of the most powerful tools for predicting long-term treatment outcome.(ABSTRACT TRUNCATED AT 400 WORDS)  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