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   3464196篇
  免费   283886篇
  国内免费   13968篇
耳鼻咽喉   48381篇
儿科学   111107篇
妇产科学   90683篇
基础医学   547989篇
口腔科学   93759篇
临床医学   307304篇
内科学   613680篇
皮肤病学   91451篇
神经病学   293685篇
特种医学   137080篇
外国民族医学   391篇
外科学   540908篇
综合类   102689篇
现状与发展   23篇
一般理论   2208篇
预防医学   288817篇
眼科学   79265篇
药学   240160篇
  23篇
中国医学   9801篇
肿瘤学   162646篇
  2021年   55142篇
  2020年   35185篇
  2019年   58255篇
  2018年   71487篇
  2017年   54416篇
  2016年   60067篇
  2015年   74320篇
  2014年   108629篇
  2013年   174110篇
  2012年   90912篇
  2011年   91035篇
  2010年   116748篇
  2009年   121348篇
  2008年   79169篇
  2007年   82669篇
  2006年   93425篇
  2005年   89355篇
  2004年   91083篇
  2003年   82397篇
  2002年   72750篇
  2001年   104647篇
  2000年   97374篇
  1999年   97620篇
  1998年   65417篇
  1997年   63071篇
  1996年   61036篇
  1995年   56454篇
  1994年   50747篇
  1993年   47207篇
  1992年   69736篇
  1991年   66965篇
  1990年   64348篇
  1989年   63515篇
  1988年   59464篇
  1987年   57902篇
  1986年   55252篇
  1985年   55178篇
  1984年   49768篇
  1983年   45794篇
  1982年   42246篇
  1981年   39708篇
  1980年   37407篇
  1979年   41877篇
  1978年   36503篇
  1977年   33472篇
  1976年   30818篇
  1975年   30061篇
  1974年   31284篇
  1973年   30089篇
  1972年   28361篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Hernia of the inferior lumbar space. A cause of back pain   总被引:1,自引:0,他引:1  
Twenty hernias of incarcerated fat at the inferior lumbar space were seen during a 23-year period. The usual complaint was a painful mass that caused a backache. The condition was more common in women and girls than in men (18 v two). The wider female pelvis creates a larger inferior lumbar space, which predisposes to the hernia. The hernia appears through a defect of the covering lumbodorsal fascia. Increased physical activity in young women seemed to be a causative factor. One patient had acute strangulation of incarcerated fat. Nineteen of the 20 hernias were treated with surgical excision and repair of the lumbodorsal fascial defect. Results of treatment were good. Though rare, hernias of the inferior lumbar space should be considered when back pain is present, particularly in a young, athletic woman.  相似文献   
992.
L. Abrahamsson  H. Hackl 《Maturitas》1981,3(3-4):225-234
53 patients from a mainly climacteric population were treated monthly with 200 mg dehydro-epiandrosterone (DHEA) oenanthate or with 1 ampoule Gynodian-Depot®. Pronounced adiposity was present in 15 of these cases. Hormonal variables were determined before the treatment and during the depot effect of the preparations in order to study the principle which supports the oestrogenic influence and any weight-reducing influence under administration of DHEA. The elimination of lowpolar oestrogens increased considerably in 4 out of 13 post-menopausal cases treated with DHEA. This effect is probably indirect and presupposes intact ovaries. The incorporation of exogenous DHEA into the excretion of 17-ketosteroids and of 17-ketogenic steroids, such as those of androsterone + aethiocholanolone, depends on the size of the initial pool inasmuch as it is higher in small initial pools than in saturated pools - the size of the pool being age-dependent.

An average weight loss of >1 kg/mth was observed under DHEA treatment in 7 out 15 adipose cases. In comparison to the other 8 adipose cases, these 7 were younger and therefore also displayed higher values for 17-ketosteroids and their individual fractions. These circumstances appeared to explain why the administration of DHEA resulted in higher levels of free plasma DHEA which, in contrast to the cases without loss of weight, also resulted in an increase of renal DHEA-sulphate clearance. It was concluded from the findings that this is the explanation for the catabolic effect of exogenous DHEA.

Post-menopausally increased FSH and LH fractions were markedly suppressed in about half of the determinations after Gynodian-Depot administration, the findings indicating that DHEA is probably involved in suppression of the LH fraction.  相似文献   

993.
(1) The estrous cycle in the rat may be used to study recurrent changes in motor behaviors and motivation which are strongly related to cyclic hormonal and CNS changes. (2) The peak in motivated behaviors occurs during a sharply defined period on the night between proestrus and estrus and is evident in facilitated wheel-running, lordosis, and intracranial self-stimulation. (3) Behaviors without a clearly motivated character do not show an estrous cyclicity. (4) The estrous cyclic variation in intracranial self-stimulation was observed at a specific locus — the pars campacta of the substantia nigra. (5) A neurochemical link between sexually motivated behavior, wheel running and intracranial self-stimulation is suggested. This link is in part dopaminergic but is probably also activated by many other systems.  相似文献   
994.
995.
996.
997.
Animal behaviour can be viewed as a stream of elements, which, once accurately described, can be counted and timed. Data acquisition techniques and tools are reviewed, and some strategies for collection and analysis of data using PC computers are suggested. Automated instruments are not satisfactory for the study of complex behaviour and as such systemic observation remains irreplaceable. IBM PC-type computers, with a wide range of analytical software (e.g., spreadsheets, statistical packages, technical graphics), are practical for data acquisition. Several systems which can satisfy different applications are reviewed. Some systems can communicate with a videorecorder, a facility which remarkably increases the accuracy of measurement; this is essential for meaningful analyses of the internal structure of behavioural streams (sequences, time patterns) or communication processes. The power of new tools enables behavioural measurement with the necessary complexity to allow a whole new set of questions to be addressed. However, it also increases demands for meaningful content and analysis of data.  相似文献   
998.
Olfactory transduction is thought to occur by processes that are mainly restricted to the specialized cilia emanating from the distal end of the receptor neuron's single dendrite. The involvement of a cAMP-based second messenger system seems likely, and a cyclic nucleotide-sensitive current has been recorded in patches of membrane from the cilia. However, the small diameter of the cilia and the high density of channels within the membrane limit the application of the patch recording technique in the cilia. We have found that the cAMP-sensitive channels also exist at a much lower density within the far more accessible dendritic membrane. Recording from on-cell patches, we have observed single-channel activity in response to extracellularly applied odor substances. The channels have a single-channel conductance of 40 pS and a reversal potential near 0 mV. These same channels are activated by treatments that elevate intracellular cyclic nucleotide concentrations. The results provide a direct demonstration that the cyclic nucleotide-gated channel is the conductance pathway for the odor-elicited current.  相似文献   
999.
As an adjunct to a European multicentre prospective study, five quality assessment (QA) exercises, spanning a period of 2.5 years, were undertaken. In these, fifteen laboratories from eight countries each performed ten haemostatic factor assays. The design of the QA exercises allowed the between-duplicate, between-day and between-laboratory coefficients of variation (CVs) to be calculated. The between-duplicate CV decreased by a factor of one quarter, and the between-day CV by a factor of one third, over the five exercises. The activated partial thromboplastin time (APTT) assay consistently showed the lowest CVs, while there was notable improvement in the between-day CVs for von Willebrand factor related antigen (vWF R:Ag) and factor VIII clotting activity (VIII:C). However, the between-laboratory CV, assessing extent of agreement between the different laboratories, did not apparently improve over the five exercises. Thus, while QA exercises may be very useful in improving the performance of haemostatic assays according to criteria which an individual laboratory can assess, improving agreement on haemostatic assay results between laboratories may be more difficult to achieve.  相似文献   
1000.
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