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   47599篇
  免费   4406篇
  国内免费   86篇
耳鼻咽喉   614篇
儿科学   1290篇
妇产科学   1318篇
基础医学   6849篇
口腔科学   1258篇
临床医学   5836篇
内科学   8338篇
皮肤病学   600篇
神经病学   3792篇
特种医学   2274篇
外国民族医学   1篇
外科学   6183篇
综合类   889篇
一般理论   23篇
预防医学   5263篇
眼科学   1090篇
药学   3541篇
  2篇
中国医学   57篇
肿瘤学   2873篇
  2021年   656篇
  2019年   638篇
  2018年   747篇
  2017年   627篇
  2016年   611篇
  2015年   706篇
  2014年   938篇
  2013年   1469篇
  2012年   2136篇
  2011年   2221篇
  2010年   1202篇
  2009年   1002篇
  2008年   1865篇
  2007年   2022篇
  2006年   2012篇
  2005年   2011篇
  2004年   1822篇
  2003年   1683篇
  2002年   1706篇
  2001年   1600篇
  2000年   1708篇
  1999年   1447篇
  1998年   663篇
  1997年   537篇
  1996年   534篇
  1995年   529篇
  1994年   465篇
  1993年   460篇
  1992年   1258篇
  1991年   1172篇
  1990年   1152篇
  1989年   1093篇
  1988年   1002篇
  1987年   1005篇
  1986年   931篇
  1985年   919篇
  1984年   724篇
  1983年   634篇
  1982年   451篇
  1981年   409篇
  1980年   403篇
  1979年   660篇
  1978年   528篇
  1977年   419篇
  1976年   410篇
  1975年   382篇
  1974年   451篇
  1973年   438篇
  1972年   450篇
  1971年   423篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Awareness of cognitive dysfunction shown by individuals with Mild Cognitive Impairment (MCI), a condition conferring risk for Alzheimer's disease (AD), is variable. Anosognosia, or unawareness of loss of function, is beginning to be recognized as an important clinical symptom of MCI. However, little is known about the brain substrates underlying this symptom. We hypothesized that MCI participants' activation of cortical midline structures (CMS) during self-appraisal would covary with level of insight into cognitive difficulties (indexed by a discrepancy score between patient and informant ratings of cognitive decline in each MCI participant). To address this hypothesis, we first compared 16 MCI participants and 16 age-matched controls, examining brain regions showing conjoint or differential BOLD response during self-appraisal. Second, we used regression to investigate the relationship between awareness of deficit in MCI and BOLD activity during self-appraisal, controlling for extent of memory impairment. Between-group comparisons indicated that MCI participants show subtly attenuated CMS activity during self-appraisal. Regression analysis revealed a highly significant relationship between BOLD response during self-appraisal and self-awareness of deficit in MCI. This finding highlights the level of anosognosia in MCI as an important predictor of response to self-appraisal in cortical midline structures, brain regions vulnerable to changes in early AD.  相似文献   
92.
Magainin 1 and magainin 2, originally isolated from African clawed frog Xenopus laevis skin, inhibit the growth of bacteria and fungi. Synthetic magainin A (MAG A) and magainin G (MAG G) are more potent against bacteria and protozoa. In order to determine the antitumor activity of these analogues, we have tested these two analogues against six small cell lung cancer (SCLC) cell lines NCI-H82, NCI-H526, NCI-H678, NCI-H735, NCI-H841, and NCI-H889, which were known to differ by more than 10-fold in their sensitivity to different chemotherapeutic agents, and four normal human fibroblast cell lines. Semiautomated 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays of the six SCLC cell lines revealed average concentrations producing 50% inhibition (IC50) values of 2.6 microM (range, 0.49-9.30 microM) for cisplatin, 2.5 microM (range, 0.39-6.00 microM) for etoposide, and 138.8 nM (range, 55.0-450.0 nM) for doxorubicin. The average IC50 of MAG A was 8.64 microM (range, 6.23-11.7 microM) and that of MAG G was 8.82 microM (range, 4.44-12.5 microM) against the SCLC cell lines. Despite a 10-fold difference in sensitivity to standard chemotherapeutic agents, the IC50 of MAG A and MAG G differs by less than 3-fold. The average IC50 against four normal human fibroblast cell lines was 21.1 microM (range, 12.7-25.6 microM) for MAG A and 29.2 microM (range, 21.3-34.8 microM) for MAG G. Combined exposure to the IC50 concentration of MAG A or MAG G plus IC50 of etoposide or cisplatin decreased the percentage of surviving SCLC cells to 29.0% (range, 26.1-31.7%). MAG A or MAG G had an additive effect when used with standard chemotherapeutic agents. These data suggest that MAG A and MAG G have in vitro antitumor activity against SCLC cell lines.  相似文献   
93.
Applied potential tomography (APT) is a new noninvasive, nonradioactive method of measuring gastric emptying, which generates profiles of emptying of liquids that are similar to those obtained simultaneously by scintigraphy and dye dilution. This study validates the ability of APT to measure emptying of a solid beefburger test meal from the stomach by comparing the results obtained with those obtained simultaneously by scintigraphy. When acid secretion was inhibited, there was a significant correlation between the two methods for the time taken for half the meal to empty from the stomach and the amount of meal emptied at different time intervals. Furthermore, the profiles of gastric emptying obtained by APT resembled those obtained by scintigraphy in most studies. If acid secretion was not inhibited, there was no correlation between values obtained by the two methods.  相似文献   
94.
A comparative study of the effectiveness of two types of lithotripter in fragmenting gall bladder stones is reported. The machines used were a Piezolith 2300, which generates shock waves by the piezoceramic principle, and a Dornier MPL 9000, which produces the shock waves by underwater spark discharge. With each machine, corresponding stones of 45 pairs of weight and volume matched calculi (median volume 0.5 cm3, median diameter 10.5 mm) obtained at cholecystectomy were treated. All stones were successfully disintegrated (fragments smaller than 2 mm) with up to 5400 (median 628) shocks with the Piezolith and 3450 (median 428) shocks with the MPL 9000 lithotripters. With the Piezolith, operating at the highest power setting, a 1.65 fold median higher number of shocks was required for stone fragmentation than with the MPL 9000 at a medium power setting. Stone volume seemed to be the only determinant which affected ease of fragmentation; composition and density of the stones as assessed by computed tomography did not seem to be governing factors.  相似文献   
95.
The human squamous carcinoma-reactive murine monoclonal antibody PF1/D was used to derive a conjugate with the Vinca derivative 4-desacetylvinblastine-3-carboxyhydrazide (PF1/D-DAVLBHYD). This immunoconjugate was shown to be largely aggregate free and there was no loss of immunoreactivity postconjugation. When tested in vivo in a 3-day-established human squamous carcinoma nude mouse xenograft model, the PF1/D-DAVLBHYD conjugate eliminated tumor growth with three injections (days 3, 6, and 9) at 2 mg/kg Vinca content. Significant tumor suppression was also observed with 0.5 mg/kg conjugate doses. In contrast, free PF1/D antibody had minimal antitumor activity and no activity was seen with identical doses of a control non-tumor-binding IgG-DAVLBHYD conjugate. Together, these data demonstrate the specificity of the PF1/D-DAVLBHYD antitumor effects.  相似文献   
96.
97.
FM sonography - a signal-processing technique that uses frequency and phase information as well as amplitude data - shows promise in evaluation of patients with diffuse liver disease. In a prospective blinded review of 37 patients with biopsy-proved liver disease and 42 healthy volunteers, FM sonography was clearly superior to traditional amplitude-based (AM) sonography in distinguishing healthy from diseased subjects. Statistically significant differences were seen in accuracy (FM, 98.7%; AM, 84.8%), sensitivity (FM, 97.3%; AM, 70.3%), and negative predictive value (FM, 97.7%; AM, 78.8%). Our data also suggest that current FM sonographic techniques cannot differentiate among histologic findings associated with different hepatic parenchymal abnormalities. It is unclear, therefore, whether FM imaging can reduce the numbers of patients who require biopsy for diagnosis or the frequency of biopsy procedures in patients with known disease.  相似文献   
98.
During the first 24 months of the Oregon Liver Transplantation Program, which began in October 1988, 94 patients were formally evaluated and 47 adults underwent 54 liver transplantations. Thirty-four percent of patients were veterans. The recipient operation lasted a mean of 7.4 hours (range: 4 to 16 hours). Veno-venous bypass was used routinely at first but selectively later (7 of the last 26 cases), resulting in reduced operating time. Hepatic artery reconstruction was end-to-end anastomosis in 52 cases and iliac conduit in 2. No arterial thrombosis occurred. Biliary reconstruction was choledochocholedochostomy in 83% and choledochojejunostomy in 17%. Biliary complications occurred in 28%. Operative mortality was 2%, and 1-year actual survival was 80%. Patients with hepatitis B fared worse, with four of six dying at a mean of 7.6 months. Overall, the median hospital stay was 30 days. Patients surviving more than 3 months had a mean Karnofsky score of 82%. No significant difference in outcome was noted in patients receiving prophylactic OKT3 monoclonal antibody (used in 45%) versus conventional immunosuppressive therapy. Overall, allograft rejection occurred in 55% of patients. Retransplantation was required in seven patients, three for primary graft nonfunction, two for uncontrolled rejection during induction therapy with OKT3, and two for graft failure secondary to recurrent hepatitis B.  相似文献   
99.
100.
Strut fixation of an extensive flail chest   总被引:2,自引:0,他引:2  
The indications for and preferred approaches to operative stabilization of posttraumatic chest wall instability are uncertain. We suggest this simple, rapid, and effective approach to surgical stabilization by Luque rod strutting of the flail segment when operation is required.  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