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   230011篇
  免费   6158篇
  国内免费   87篇
耳鼻咽喉   1846篇
儿科学   8071篇
妇产科学   4520篇
基础医学   24516篇
口腔科学   3081篇
临床医学   18996篇
内科学   40316篇
皮肤病学   1387篇
神经病学   20922篇
特种医学   11169篇
外国民族医学   3篇
外科学   36282篇
综合类   3257篇
一般理论   34篇
预防医学   23840篇
眼科学   4068篇
药学   13436篇
  2篇
中国医学   688篇
肿瘤学   19822篇
  2022年   434篇
  2021年   1039篇
  2020年   571篇
  2019年   948篇
  2018年   22851篇
  2017年   18090篇
  2016年   20192篇
  2015年   1811篇
  2014年   2025篇
  2013年   2601篇
  2012年   9575篇
  2011年   23542篇
  2010年   20164篇
  2009年   12656篇
  2008年   21629篇
  2007年   23993篇
  2006年   2901篇
  2005年   4470篇
  2004年   5452篇
  2003年   6234篇
  2002年   4406篇
  2001年   2067篇
  2000年   2286篇
  1999年   1773篇
  1998年   877篇
  1997年   744篇
  1996年   653篇
  1995年   656篇
  1994年   573篇
  1993年   540篇
  1992年   1409篇
  1991年   1385篇
  1990年   1406篇
  1989年   1277篇
  1988年   1148篇
  1987年   1145篇
  1986年   1039篇
  1985年   1031篇
  1984年   799篇
  1983年   713篇
  1982年   520篇
  1980年   487篇
  1979年   723篇
  1978年   604篇
  1977年   463篇
  1976年   460篇
  1974年   538篇
  1973年   505篇
  1972年   513篇
  1971年   482篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Trypsin, when added to a bioassay for tumoricidal macrophages, produced killing of tumor cells. Trypsin cleaved fetal calf serum proteins to produce a protein fragment that activated macrophages to lyse tumor cells. Diisopropyl fluorophosphate-inhibited trypsin did not produce tumoricidal macrophages either by direct action on the macrophage or by action on serum proteins. The macrophage activation factors produced from serum proteins were fractionated into molecular weight ranges of 150,000, 68,000, and 30,000-5000. The effects of neutral proteinases and proteinase inhibitors on the ability of macrophages to lyse tumor cells is discussed.This study was supported by NSF grant PCM 8007869.  相似文献   
993.
A family is described in which incontinentia pigmenti (IP) is variably expressed in both sexes, compatible with either autosomal dominant or X linked dominant inheritance. This is the first reported instance of an affected male with a positive family history. Immunological studies of the proband showed no significant alteration of immune function. Cytogenetic investigations of the proband and her affected brother and mother revealed no unusual propensity for chromosome breaks or gaps and no enhancement of sister chromatid exchanges.  相似文献   
994.
Cutaneous vascular conductance (CVC) decreases during isometric handgrip exercise in heat stressed individuals, and we hypothesized that central command is involved in this response. Seven subjects performed 2 min of isometric handgrip exercise (35% of maximal voluntary contraction) followed by postexercise ischaemia in normothermia and during heat stress (increase in internal temperature ∼1°C). To augment the contribution of central command independent of force generation, on a separate day the protocol was repeated following partial neuromuscular blockade (PNB; i.v. cisatracurium). Forearm skin blood flow was measured by laser-Doppler flowmetry, and CVC was the ratio of skin blood flow to mean arterial pressure. The PNB attenuated force production despite encouragement to attain the same workload. During the heat stress trials, isometric exercise decreased CVC by ∼12% for both conditions, but did not change CVC in either of the normothermic trials. During isometric exercise in the heat, the increase in mean arterial pressure (MAP) was greater during the control trial relative to the PNB trial (31.0 ± 9.8 versus 18.6 ± 6.4 mmHg, P < 0.01), while the elevation of heart rate tended to be lower (19.4 ± 10.4 versus 27.4 ± 8.1 b.p.m., P = 0.15). During postexercise ischaemia, CVC and MAP returned to pre-exercise levels in the PNB trial but remained reduced in the control trial. These findings suggest that central command, as well as muscle metabo-sensitive afferent stimulation, contributes to forearm cutaneous vascular responses in heat stressed humans.  相似文献   
995.
OBJECTIVE: To estimate HIV and sexually transmitted disease (STD) prevalence and behavioral risk characteristics of men who have sex with men (MSM) in Chennai, India. METHODS: A cross-sectional population-based random sample survey was conducted in 2001. Randomly selected residents of 30 slums in Chennai were interviewed for behavioral risk factors through face-to-face interviews. Sera and urine were examined for syphilis, HIV-1, gonorrhea, and chlamydia. Logistic regression analyses were used to assess associations between MSM status and HIV infection and to identify risk characteristics of MSM. RESULTS: Of 774 men, 46 reported (5.9%) sex with other men. MSM were more likely to be seropositive for HIV (odds ratio [OR] = 8.57; 95% confidence interval [CI]: 1.83, 40.23) and were more likely to have a history of STD (OR = 2.66; 95% CI: 1.18, 6.02) than non-MSM. Men who used illicit drugs in past 3 months (adjusted odds ratio [AOR] = 4.01; 95% CI: 1.92, 8.41), ever exchanged money for sex (AOR = 3.93; 95% CI: 1.97, 7.84), or were ever tested for HIV (AOR = 3.72; 95% CI: 1.34, 10.34) were significantly more likely to report sex with men. CONCLUSIONS: MSM in Chennai slums are at high risk for HIV. HIV prevention strategies aimed at changing unsafe drug and sexual practices should target the general population of men, with specific attention to areas with high rates of MSM.  相似文献   
996.
Sohi HH  Maleki M 《Virus genes》2004,29(3):353-358
Rhizomania a viral disease, caused by beet necrotic yellow vein benyvirus (BNYVV), is now widely spread, throughout the sugar beet growing areas of Iran. Genomes of BNYVV are composed of five RNA molecules with specific functions. In this study sequence analyses were conducted on the major coat protein gene (CP21), and parts of RNA3 and RNA4 of an Iranian strain of BNYVV from the Fars province. Sequence alignments of Iran Fars CP21 with other isolates showed closed similarities at nucleotide and amino acid levels with BNYVV pathotype A isolates; S from Japan, and YU2 from Yugoslavia. These results suggest that Iran-Fars isolate probably originated from Asia or neighboring European countries rather than from Germany or France.  相似文献   
997.
BACKGROUND: Regular use of inhaled corticosteroids (ICSs) can improve asthma symptoms and prevent exacerbations. However, overall adherence is poor among patients with asthma. Objective To estimate the proportion of poor asthma-related outcomes attributable to ICS nonadherence. METHODS: We retrospectively identified 405 adults age 18 to 50 years who had asthma and were members of a large health maintenance organization in southeast Michigan between January 1, 1999, and December 31, 2001. Adherence indices were calculated by using medical records and pharmacy claims. The main outcomes were the number of asthma-related outpatient visits, emergency department visits, and hospitalizations, as well as the frequency of oral steroid use. RESULTS: Overall adherence to ICS was approximately 50%. Adherence to ICS was significantly and negatively correlated with the number of emergency department visits (correlation coefficient [ R ] = -0.159), the number of fills of an oral steroid ( R = -0.179), and the total days' supply of oral steroid ( R = -0.154). After adjusting for potential confounders, including the prescribed amount of ICS, each 25% increase in the proportion of time without ICS medication resulted in a doubling of the rate of asthma-related hospitalization (relative rate, 2.01; 95% CI, 1.06-3.79). During the study period, there were 80 asthma-related hospitalizations; an estimated 32 hospitalizations would have occurred were there no gaps in medication use (60% reduction). CONCLUSIONS: Adherence to ICS is poor among adult patients with asthma and is correlated with several poor asthma-related outcomes. Less than perfect adherence to ICS appears to account for the majority of asthma-related hospitalizations.  相似文献   
998.
The ability to provide the best treatment for breast cancer depends on establishing whether or not the cancer has spread to the lymph nodes under the arm. Conventional assessment requires tissue removal, preparation, and expert microscopic interpretation. In this study, elastic scattering spectroscopy (ESS) is used to interrogate excised nodes with pulsed broadband illumination and collection of the backscattered light. Multiple spectra are taken from 139 excised nodes (53 containing cancer) in 68 patients, and spectral analysis is performed using a combination of principal component analysis and linear discriminant analysis to correlate the spectra with conventional histology. The data are divided into training and test sets. In test sets containing spectra from only normal nodes and nodes with complete replacement by cancer, ESS detects the spectra from cancerous nodes with 84% sensitivity and 91% specificity (per-spectrum analysis). In test sets that included normal nodes and nodes with partial as well as complete replacement by cancer, ESS detects the nodes with cancer with an average sensitivity of 75% and specificity of 89% (per-node analysis). These results are comparable to those from conventional touch imprint cytology and frozen section histology, but do not require an expert pathologist for interpretation. With automation of the technique, results could be made available almost instantaneously. ESS is a promising technique for the rapid, accurate, and straightforward detection of metastases in excised sentinel lymph nodes.  相似文献   
999.
1000.
Human adenocarcinoma (AC) is the most frequently diagnosed human lung cancer, and its absolute incidence is increasing dramatically. Compared to human lung AC, the A/J mouse-urethane model exhibits similar histological appearance and molecular changes. We examined the gene expression profiles of human and murine lung tissues (normal or AC) and compared the two species' datasets after aligning approximately 7500 orthologous genes. A list of 409 gene classifiers (P value <0.0001), common to both species (joint classifiers), showed significant, positive correlation in expression levels between the two species. A number of previously reported expression changes were recapitulated in both species, such as changes in glycolytic enzymes and cell-cycle proteins. Unexpectedly, joint classifiers in angiogenesis were uniformly down-regulated in tumor tissues. The eicosanoid pathway enzymes prostacyclin synthase (PGIS) and inducible prostaglandin E(2) synthase (PGES) were joint classifiers that showed opposite effects in lung AC (PGIS down-regulated; PGES up-regulated). Finally, tissue microarrays identified the same protein expression pattern for PGIS and PGES in 108 different non-small cell lung cancer biopsies, and the detection of PGIS had statistically significant prognostic value in patient survival. Thus, the A/J mouse-urethane model reflects significant molecular details of human lung AC, and comparison of changes in orthologous gene expression may provide novel insights into lung carcinogenesis.  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