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   15231篇
  免费   914篇
  国内免费   74篇
耳鼻咽喉   75篇
儿科学   557篇
妇产科学   367篇
基础医学   2095篇
口腔科学   268篇
临床医学   1461篇
内科学   3297篇
皮肤病学   373篇
神经病学   1526篇
特种医学   323篇
外科学   1696篇
综合类   87篇
一般理论   16篇
预防医学   1235篇
眼科学   306篇
药学   989篇
中国医学   25篇
肿瘤学   1523篇
  2024年   13篇
  2023年   152篇
  2022年   227篇
  2021年   519篇
  2020年   315篇
  2019年   443篇
  2018年   488篇
  2017年   391篇
  2016年   386篇
  2015年   479篇
  2014年   628篇
  2013年   813篇
  2012年   1261篇
  2011年   1179篇
  2010年   704篇
  2009年   597篇
  2008年   1018篇
  2007年   1025篇
  2006年   972篇
  2005年   888篇
  2004年   853篇
  2003年   797篇
  2002年   646篇
  2001年   111篇
  2000年   100篇
  1999年   118篇
  1998年   114篇
  1997年   102篇
  1996年   94篇
  1995年   69篇
  1994年   58篇
  1993年   63篇
  1992年   61篇
  1991年   50篇
  1990年   46篇
  1989年   33篇
  1988年   30篇
  1987年   35篇
  1986年   29篇
  1985年   45篇
  1984年   28篇
  1983年   24篇
  1982年   19篇
  1980年   20篇
  1979年   16篇
  1977年   15篇
  1972年   16篇
  1971年   16篇
  1970年   13篇
  1965年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
A recent study put forward the hypothesis that microlithiasis may represent an early stage in the development of biliary calculi. It is an established fact that cholesterol crystals are the product of an inevitable stage in the sequence leading to gallstone formation. To test the hypothesis stated above ten patients affected by gallbladder cholesterol microlithiasis (CM) were examined in the lipid composition of the bile, the cholesterol saturation index and the presence of cholesterol crystals being calculated. The results were compared with those of 14 patients affected by pigment microliths, 24 with larger stones (LS) and ten control patients. The cholesterol saturation index was above one in all CM patients, whereas in some LS patients the gall-bladder bile was not supersaturated. Cholesterol crystals were observed in the gallbladders of all CM patients and seven LS patients. These results would seem to provide support for the hypothesis of microcalculi as being "young stones", with the bile of CM patients maintaining the conditions leading to gallstone formation.  相似文献   
62.
Although the numbers of newly reported diagnoses of AIDS decreased in the 1990s, it is not clear whether they reflect a decreasing number of new HIV infections. Direct measurement of HIV incidence through follow-up cohort studies is difficult and costly. We estimated HIV incidence and trends in incidence among men who have sex with men (MSM) and heterosexual men and women at clinics for sexually transmitted diseases (STDs) by using a recently developed serologic testing algorithm that requires only a single blood specimen. Cross-sectional anonymous serosurveys were conducted at 13 STD clinics in nine cities in the United States from 1991 through 1997. Before anonymous HIV testing, demographic and clinical information was abstracted. Of 129,774 specimens tested, 362 (0.28%) were from persons estimated to be recently infected. Incidence among MSM was 7.1% (95% confidence interval (CI): 4.8-10.3), 14 times higher than that among heterosexuals, which was 0.5% (CI: 0.4- 0.7). Incidence among MSM and heterosexuals remained unchanged during the time studied. Decreasing rates of new AIDS diagnoses in the 1990s do not reflect stable rates of new HIV infections among MSM and heterosexual patients attending these clinics.  相似文献   
63.
BACKGROUND: Global ubiquitination in human semen has been found to negatively correlate with standard semen parameters, indicating that ubiquitination can be considered a marker of poor semen quality. However, the inclusion of all semen components in the analysis may be misleading on the biological significance of ubiquitination of sperm cells. We have recently demonstrated the variable presence of bodies of different size, with the highest concentration in oligoasthenoteratozoospermia. The purpose of the present study was to evaluate the relationship between ubiquitination and standard semen parameters, after distinguishing between ubiquitinated sperm and bodies in each sample. METHODS: Ubiquitination was evaluated by flow cytometric sperm ubiquitin tag immunoassay (SUTI) in sperm samples from 45 subjects. Semen analysis was performed according to WHO (1999) guidelines. RESULTS: When only ubiquitinated sperm were considered, a positive correlation with number, motility and normal morphology was found. When correlation was evaluated considering the percentage of ubiquitinated bodies, a negative correlation was found with good semen quality. CONCLUSIONS: Results indicate that the negative correlations previously found between global semen ubiquitination and parameters of semen analysis are mainly driven by components other than sperm. The positive correlation between sperm ubiquitination and good quality parameters suggests a previously unrecognized role for sperm ubiquitination.  相似文献   
64.
A new type of swab (Cellswab; Cellomeda, Turku, Finland), utilizing a highly absorbent cellulose viscose sponge material, was compared to some traditional swabs. The survival of 14 aerobic and 10 anaerobic and microaerophilic bacterial species in the Cellswab, two commercial swab transport systems (Copan, Brescia, Italy, and Orion Diagnostica, Espoo, Finland), and one Dacron swab (Technical Service Consultants Ltd. [TSC], Heywood, United Kingdom) was evaluated. Bacteria were suspended in broth, into which the swabs were dipped. The Cellswab absorbed 1.3 times more fluid and released 3.5 times more fluid upon plating than the other swabs. Aerobic bacteria were stored in dry tubes, the others in transport medium, at 4 degrees C and room temperature (RT), for up to 14 days. Swab samples were transferred to plates at 0, 1, 2, 4, 7, and 14 days. For 10 strains the Cellswab yielded > or =10% of the original CFU for longer than all the other swabs. In the clinical study, the ability of the Cellswab to detect beta-hemolytic streptococci from throat samples (n = 995) was compared to that of the TSC Dacron swab. The swabs performed equally, both when their samples were transferred to plates immediately and after storage for 1 day at 4 degrees C or RT. The changes in normal microbiota after storage were also similar. The Cellswab was found to perform at least as well as ordinary swabs. It was better at storing fastidious strains, and at keeping bacteria viable for long storage times; it might well be a useful replacement or complement to ordinary swabs.  相似文献   
65.

Background  

Osteoclasts (OCs) are involved in rheumatoid arthritis and in several pathologies associated with bone loss. Recent results support the concept that some medicinal plants and derived natural products are of great interest for developing therapeutic strategies against bone disorders, including rheumatoid arthritis and osteoporosis. In this study we determined whether extracts of Emblica officinalis fruits display activity of possible interest for the treatment of rheumatoid arthritis and osteoporosis by activating programmed cell death of human primary osteoclasts.  相似文献   
66.
A properly engineered biomaterial for dental/orthopaedic applications must induce specific responses from the osteoblasts at the implant site. A most desirable response is an efficient adhesion, as it represents the first phase in the cell/material interaction and the quality of this phase will influence the cell's capacity to organize into a new functional tissue. The four osteoblast-adhesive peptides discussed in this paper are mapped on the 339-364 sequence (339MAPRPSLAKKQRFRHRNRKGYRSQRG364) located in the primary heparin-binding site of human vitronectin (HVP). Adsorbed on a polystyrene scaffold, these peptides display different adhesive activities towards osteoblasts. In this paper we report on the structural analysis in solution of the peptides through NMR and computational techniques. We find that the peptides with the highest adhesive activities display a hydrophobic patch opposite to the charged surface candidate to interact with heparin. These findings suggest that the peptides might adsorb on the polystyrene support in a favourable orientation for their activity. Furthermore, molecular models obtained for the four peptides in solution were used in rigid docking simulations with a heparin model. Assuming that the peptide solution conformations are not very different from the polystyrene-adsorbed structures, the simulations reveal that peptide adhesive activity is also affected by the number of ionic interactions and spacing between charged residues.  相似文献   
67.
The purpose of this study was to assess the impact of genetic self-knowledge (nondisease genotype information) on individual self-concept and Health Orientation Scale (HOS). Adult volunteers (n=257) were recruited from an ongoing genetic association study identifying muscle quantitative trait loci (QTLs). Participants completed psychosocial assessments before and after 12 weeks of resistance training of the nondominant arm. At study exit, a genetic counselor informed participants of genetic test results on three to four genes that have an association with muscle-related traits, and counseled subjects on the potential significance of these findings. The second psychosocial assessment was performed immediately following this counseling session. The Tennessee Self-Concept Scale v.2 (TSCS:2) and the HOS showed female subjects to have a significantly greater positive change between first and second assessments, relative to male subjects. Most self-concept subscales improved significantly, when 'neutral' genotypes (no anticipated beneficial or deleterious impact) were reported, compared to positive genotypes. TSCS:2 subscales showing improvement included: total (P=0.013); physical (P=0.004); satisfaction (P=0.019); and behavioral (P=0.047). HOS subscales showing improvement included health image concern (P=0.006); and health expectations (P=0.047). In conclusion, these results suggest that genetic self-knowledge affects self-concept, consistent with the 'attribution' theory. Individuals who received neutral genetic information attributed positive changes from the exercise program to their own abilities, while those who received positive information were more likely to attribute positive changes to their genetics. This study is limited by the ability to determine the direction of the impact of nondisease genetic information presented to participants.  相似文献   
68.
Klein (Arch. Gen. Psychiatry 50, 306-317, 1993) suggests that panic attacks are the result of a defective 'suffocation alarm' threshold that presents with carbon dioxide (CO(2)) hypersensitivity, exaggerated ventilatory response and panic in panic disorder (PD) patients. Serotonergic deficiencies enhance this ventilatory response in PD patients, as per 'suffocation alarm' theory predictions, suggesting that serotonin (5-HT) normalizes the ventilatory response. Other research supports a serotonin system-mediated stimulation of ventilation. Knowledge of 5-HT's role on ventilatory output and its neurophysiological sources impacts on the 'suffocation alarm' theory validity and predictive value. We used tryptophan depletion (TRP-) in concert with a modified Read rebreathing test to determine the effect of deficient serotonergic modulation on the central and peripheral chemoreflex threshold and sensitivity of response to CO(2) in 11 healthy men. TRP- did not affect central or peripheral chemoreflex threshold or sensitivity of response to CO(2). However, basal ventilation was significantly elevated during TRP-. In contrast to 'suffocation alarm' theory predictions, decreased 5-HT neurotransmission does not significantly affect the respiratory chemoreflex response to CO(2), impacting on non-chemoreflex drives to breathe. Panic associated respiratory abnormalities may be related to defective 5-HT modulation of non-chemoreflex drives to breathe, unrelated to any respiratory chemoreflex abnormality.  相似文献   
69.
70.
We report a case of a 42-yr-old woman with Langerhans cell histiocytosis (LCH) confined to the thyroid and associated with lymphocytic thyroiditis and a papillary microcarcinoma. This patient remains free of symptoms 14 mo after surgery. Thyroid LCH is rare. In children, it usually occurs as part of a multisystemic disease, whereas it is usually exclusive in adults. Isolated thyroid LCH is frequently associated with another thyroid disease, especially lymphocytic thyroiditis, suggesting that it is a reactive process rather than a neoplastic proliferation. The prognosis of isolated thyroid LCH is good. However, because it can rarely precede or reveal a multisystemic disease, additional investigations as well as a prolonged follow-up are justified.  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