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   16289篇
  免费   2276篇
  国内免费   8篇
  2021年   158篇
  2018年   168篇
  2017年   150篇
  2016年   255篇
  2015年   385篇
  2014年   484篇
  2013年   664篇
  2012年   740篇
  2011年   710篇
  2010年   453篇
  2009年   430篇
  2008年   608篇
  2007年   618篇
  2006年   562篇
  2005年   519篇
  2004年   559篇
  2003年   559篇
  2002年   509篇
  2001年   544篇
  2000年   528篇
  1999年   450篇
  1998年   250篇
  1997年   230篇
  1996年   206篇
  1995年   228篇
  1994年   215篇
  1993年   190篇
  1992年   374篇
  1991年   345篇
  1990年   373篇
  1989年   317篇
  1988年   307篇
  1987年   315篇
  1986年   301篇
  1985年   318篇
  1984年   257篇
  1983年   228篇
  1982年   200篇
  1981年   203篇
  1980年   166篇
  1979年   277篇
  1978年   228篇
  1977年   185篇
  1976年   173篇
  1975年   180篇
  1974年   195篇
  1973年   168篇
  1972年   176篇
  1970年   153篇
  1969年   159篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
We compared two different methods of observing trainees at work in general practice: the traditional one of a senior or training general practitioner sitting in during selected surgeries and the more modern video recording, with the patients'' written consent. Patients who had experienced the presence of a second doctor during the consultation were less likely to show an increase in arousal after their consultations than those who had been recorded on video. Patients who refused consent to be recorded were more highly stressed than those who agreed and showed smaller decreases in stress after consultations. The presence of two doctors generated fewer reductions in stress after the consultation than video recording did, but this was a non-significant trend. The group that was recorded on video did not differ appreciably from a control group in changes in stress or arousal.  相似文献   
24.
25.
The feeding of young by parents was observed in three color-banded families of wild Mexican jays. The development of indiscriminate feeding of each other's young by the parents began well before the young left the nest. These observations suggest that reciprocal feeding is not an accident and that it might be more beneficial than exclusive feeding of own young for parent Mexican Jays. The membership hypothesis and the helper-resource hypothesis are proposed as possible explanations.  相似文献   
26.
Acetylcholine, oxotremorine and carbachol, compounds that exhibit muscarinic agonist activity, maximally inhibited basal prolactin secretion from GH3 cells by approx. 50% and intracellular cyclic AMP levels by approx. 20%. Both parameters were inhibited with similar potencies by each agonist. These inhibitory effects were blocked by a muscarinic but not by a nicotinic receptor antagonist. In the presence of VIP or IBMX, which raise intracellular cyclic AMP levels and stimulate hormone release, the degree of muscarinic inhibition was increased, but the potency remained unchanged. Similar changes in the secretory rate of prolactin and growth hormone occurred in these and in cell perifusion experiments. These results suggest that the inhibition of hormone secretion from GH3 cells by muscarinic agonists is mediated by a decrease in intracellular cyclic AMP levels.  相似文献   
27.
Type III glycogen storage disease is caused by a deficiency of glycogen debranching-enzyme activity. Many patients with this disease have both liver and muscle involvement, whereas others have only liver involvement without clinical or laboratory evidence of myopathy. To improve our understanding of the molecular basis of the disease, debranching enzyme was purified 238-fold from porcine skeletal muscle. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis the purified enzyme gave a single band with a relative molecular weight of 160,000 that migrated to the same position as purified rabbit-muscle debranching enzyme. Antiserum against porcine debranching enzyme was prepared in rabbit. The antiserum reacted against porcine debranching enzyme with a single precipitin line and demonstrated a reaction having complete identity to those of both the enzyme present in crude muscle and the enzyme present in liver extracts. Incubation of antiserum with purified porcine debranching enzyme inhibited almost all enzyme activity, whereas such treatment with preimmune serum had little effect. The antiserum also inhibited debranching-enzyme activity in crude liver extracts from both pigs and humans to the same extent as was observed in muscle. Immunoblot analysis probed with anti-porcine-muscle debranching-enzyme antiserum showed that the antiserum can detect debranching enzyme in both human muscle and human liver. The bands detected in human samples by the antiserum were the same size as the one detected in porcine muscle. Five patients with Type III and six patients with other types of glycogen storage disease were subjected to immunoblot analysis. Although anti-porcine antiserum detected specific bands in all liver and muscle samples from patients with other types of glycogen storage disease (Types I, II, and IX), the antiserum detected no cross-reactive material in any of the liver or muscle samples from patients with Type III glycogen storage disease. These data indicate (1) immunochemical similarity of debranching enzyme in liver and muscle and (2) that deficiency of debranching-enzyme activity in Type III glycogen storage disease is due to absence of debrancher protein in the patients that we studied.  相似文献   
28.
Twenty-six nail deformities secondary to ganglions of the distal interphalangeal joint were retrospectively reviewed to assess the important aspects of their management. The patients' ages ranged from 41 to 79 years. The long and index fingers were most commonly involved. A depression or groove was present in 23 of 26 digits reviewed. Two had gross disruption of the nail. Fifty-eight percent of the cysts had spontaneously drained or had been drained by the patient or a physician preoperatively. Degenerative arthritic changes were seen in 87 percent of those with x-rays or a radiology report available. Most underwent surgical removal of the cyst and debridement of associated osteophytes of the distal interphalangeal joint. The cyst was located above the germinal matrix in all but two digits. Osteophytes were found in all 20 digits in which the joint was explored. No recurrences were seen in those available for postoperative follow-up (22 of 25). Normal nail growth was found in 14 of 22, although follow-up was short in one. All eight postoperative nail deformities were quite mild and of little concern to the patient. There was no correlation between preoperative cyst drainage and aesthetic postoperative nail growth. Nail removal at the time of surgery appeared to be unnecessary unless the nail was grossly disrupted.  相似文献   
29.
30.
D P Bajpayee  K I Brown 《Steroids》1971,18(4):491-503
Solvent partitioning, column chromatography on activated alumina, and Ittrich extraction of Kober chromogens were employed to isolate, identify and quantitate estrone, estradiol-17B and estriol from blood of individual turkey hens. The intravaginal tetrazolium method was used to estimate the biological potencies of the three fractions separated chromatographically. The data show that estrone is the main estrogen present in heart blood of laying turkeys, with lesser amounts of estradiol-17B and estriol. Data are presented on the accuracy, precision, sensitivity, and specificity of the methodology used.  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