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   12227篇
  免费   740篇
  国内免费   6篇
  2023年   106篇
  2022年   110篇
  2021年   224篇
  2020年   204篇
  2019年   209篇
  2018年   420篇
  2017年   380篇
  2016年   511篇
  2015年   762篇
  2014年   756篇
  2013年   915篇
  2012年   1095篇
  2011年   947篇
  2010年   620篇
  2009年   423篇
  2008年   742篇
  2007年   662篇
  2006年   611篇
  2005年   530篇
  2004年   462篇
  2003年   415篇
  2002年   388篇
  2001年   175篇
  2000年   159篇
  1999年   113篇
  1998年   83篇
  1997年   43篇
  1996年   59篇
  1995年   60篇
  1994年   33篇
  1993年   42篇
  1992年   75篇
  1991年   61篇
  1990年   52篇
  1989年   39篇
  1988年   42篇
  1987年   42篇
  1986年   29篇
  1985年   49篇
  1984年   38篇
  1983年   18篇
  1982年   24篇
  1981年   24篇
  1980年   23篇
  1979年   22篇
  1978年   22篇
  1977年   23篇
  1975年   16篇
  1974年   15篇
  1973年   15篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
51.
A series of 35 patients have been submitted to microsurgical callosotomy since February 1978, their age ranging from 6 to 42 years. The surgical procedure consisted either of a frontal parasagittal trephination or a larger frontoparietal rectangular craniotomy to allow the investigation of the surgical areas of the hemispheres with electrocorticography under local anesthesia. This allowed us to better follow the electrographic abnormalities and plan the extent of the callosal section suited to each case, in particular rostral and genual section, section of the trunk only or subtotal section sparing the splenium. In 2 cases, cortical resection was associated with the split. The callosal fibers which were divided by careful section under the resected portion provided a critical postoperative control of the extent of the lesion. Results and selection criteria will also be analyzed.  相似文献   
52.
Enterobius vermicularis eggs were found in human coprolites collected in the archaeological site of Caserones, Tarapaca Valley, Chile, dating from 400 BC to 800 AD. The human pinworm had already been found in other pre-historic archaeological sites in America, and its introduction in this continent is discussed.  相似文献   
53.
N-methyl-N'-nitro-N-nitrosoguanidine (nitrosoguanidine) and to a lesser extent UV radiation are very mutagenic for Gibberella microconidia. The recommended nitrosoguanidine doses lead to much higher frequencies of mutants than are found in other microorganisms. The frequency of mutants among the survivors increases linearly with the nitrosoguanidine dose (molar concentration X time); the absolute number of viable mutants in a given population reaches a maximum for a dose of ca. 0.7 M X s. The microconidia are uninucleate. The onset of germination brings about increased lethality of nitrosoguanidine, but it does not modify the action of UV radiation. Mycelia are more resistant than spores to both agents. Visible illumination effectively prevents lethality when given immediately after UV radiation. Auxotrophs and color mutants are very easily obtained. Pink adenine auxotrophs and several classes of color mutants are affected in the biosynthesis of the carotenoid pigment, neurosporaxanthin.  相似文献   
54.
The role of ADP in the regulation of Ca2+ efflux in rat brain mitochondria was investigated. ADP was shown to inhibit Ruthenium-Red-insensitive H+- and Na+-dependent Ca2+-efflux rates if Pi was present, but had no effect in the absence of Pi. The primary effect of ADP is an inhibition of Pi efflux, and therefore it allows the formation of a matrix Ca2+-Pi complex at concentrations above 0.2 mM-Pi and 25 nmol of Ca2+/mg of protein, which maintains a constant free matrix Ca2+ concentration. ADP inhibition of Pi and Ca2+ efflux is nucleotide-specific, since in the presence of oligomycin and an inhibitor of adenylate kinase ATP does not substitute for ADP, is dependent on the amount of ADP present, and requires ADP concentrations in excess of the concentrations of translocase binding sites. Brain mitochondria incubated with 0.2 mM-Pi and ADP showed Ca2+-efflux rates dependent on Ca2+ loads at Ca2+ concentrations below those required for the formation of a Pi-Ca2+ complex, and behaved as perfect cytosolic buffers exclusively at high Ca2+ loads. The possible role of brain mitochondrial Ca2+ in the regulation of the tricarboxylic acid-cycle enzymes and in buffering cytosolic Ca2+ is discussed.  相似文献   
55.
The conditions under which an oscillatory behaviour is observed during net hydrolysis or synthesis of ATP in chromatophores of Rhodospirillum rubrum FR1 are described. In the case of ATPase the oscillations are observed at low temperature (ca. 11°C) in the dark after an initial transient behaviour. These oscillations are attenuated or disappear by the addition of an uncoupler.Oscillations are also observed during ATP synthesis. At 3°C the oscillations appear spontaneously if photophosphorylation is measured during a sufficiently long time. At 30°C the mere intercalation of a dark period also at 30°C is sufficient to trigger the oscillations in the following light period.Abbreviations Bchl Bacteriochlorophyll - FCCP carbonyl cyanide p-trifluoromethoxyphenyl hydrazone - PMS phenazine methosulfate - TMPD, N,N,N,N tetramethyl-1,4-phenylenediamine Dedicated to Prof. Dr. Gerhart Drews as a homage for his permanent example as hard worker and careful scientist and also for his remarkable human quality  相似文献   
56.
The fertility of spermatozoa from the different epididymal segments of hamsters was tested by in-vivo insemination. Caput and proximal corpus spermatozoa were non-fertile; spermatozoa from the distal corpus epididymidis fertilized 13% (38/290) oocytes and those from the proximal and distal cauda epididymidis 71 and 87%, respectively. When tested by in-vitro insemination, distal corpus spermatozoa penetrated 44% of oocytes while those from the distal cauda fertilized 87% of oocytes. Spermatozoa from the distal corpus recovered in Medium BMOC fertilized 13% (28/219) of oocytes in vivo, while those mixed with an epididymal protein preparation (0.8 mg protein/ml) fertilized 24% (49/204; P less than 0.01) of oocytes. When distal corpus spermatozoa were inseminated in vivo with 0.8 mg epididymal protein preparation 34% (31/90) oocytes were fertilized and only 22% (23/103; P less than 0.05) oocytes were fertilized when the proteins were obtained from epididymides of animals castrated for 30 days. When distal corpus spermatozoa were preincubated for 5 h in medium without (control) or with protein preparation (0.8 or 1.6 mg protein/ml), a significant increase in in-vitro oocyte penetration was found (25 compared with 45%; P less than 0.05) when the protein was present at 1.6 mg/ml. These results confirm and extend previous observations suggesting a role for androgen-dependent glycoproteins secreted by the epididymis in the acquisition of fertilizing ability that occurs during sperm maturation.  相似文献   
57.
58.
59.
60.
A critical survey is made of human mycoses diagnosed in European Portugal and in the Portuguese Overseas Provinces. Dermatophyte infections and pityriasis versicolor are commom in the entire territory. The more frequently isolated dermatophytes in Continental Portugal wereTrichophyton violaceum, Microsporum canis, Trichophyton tonsurans andTrichophyton schoenleinii, in the scalp andTrichophyton rubrum, Trichophyton mentagrophytes, Trichophyton megninii andEpidermophyton floccosum in the other body sites. In the Overseas Provinces the species found in white people were very much the same, whereas in negroes mainlyMicrosporum audouinii andT. violaceum in Mozambique,M. audouinii in Angola, andTrichophyton soudanense, M. audouinii andT. rubrum in Guinea were identified.In Continental Portugal cases of candidiasis, mycetoma, aspergillosis, sporotrichosis and cryptococcosis were described in patients who had never been outside Europe; and tinea nigra, African histoplasmosis and South-American blastomycosis in individuals who live or lived in India, Africa and Brazil.The first case of North-American blastomycosis was reported in Mozambique.  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