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   5929篇
  免费   195篇
  6124篇
  2023年   108篇
  2021年   47篇
  2020年   41篇
  2019年   53篇
  2018年   60篇
  2017年   48篇
  2016年   71篇
  2015年   137篇
  2014年   123篇
  2013年   548篇
  2012年   263篇
  2011年   213篇
  2010年   145篇
  2009年   126篇
  2008年   182篇
  2007年   213篇
  2006年   141篇
  2005年   123篇
  2004年   137篇
  2003年   106篇
  2002年   112篇
  2001年   47篇
  2000年   44篇
  1999年   68篇
  1998年   51篇
  1997年   53篇
  1996年   42篇
  1995年   47篇
  1993年   46篇
  1992年   44篇
  1990年   45篇
  1989年   89篇
  1988年   83篇
  1987年   109篇
  1986年   76篇
  1985年   80篇
  1984年   68篇
  1983年   48篇
  1982年   64篇
  1981年   65篇
  1980年   60篇
  1979年   73篇
  1978年   76篇
  1977年   79篇
  1976年   98篇
  1975年   93篇
  1974年   70篇
  1973年   46篇
  1972年   44篇
  1964年   41篇
排序方式: 共有6124条查询结果,搜索用时 15 毫秒
11.
Ohne ZusammenfassungDieser Vortrag war für die (unter dem Druck der Verhältnisse abgesagte) Gesellschaftstagung vom 4. und 5. IX. d. J. zu München bestimmt.  相似文献   
12.
Soil inhabiting pests and rot of feeding roots of sugar beet depending on rotation - Results of a long-term trial Over a period of 17 years a trial was carried out with sugar beet, cereals and oilseed rape in different crop rotations on a field near Göttingen (Lower Saxony). The frequency of sugar beet in the rotation was 17, 25, 33 and 67 %. In absence of beet nematodes, root and sugar yield of the beet decreased after repeated growing of sugar beet in short rotations compared to variants with long rotations. Sugar content and beet quality were only slightly influenced. By applying a bioassay (BW-Test) with young beet plants in the greenhouse it was shown that increasing infections on the tips of rootlets of the beet plants were the cause for decreasing beet yield in close rotations. Mortality of young beet plants and progress of infection in the test indicated roughly the quantity of pathogenic fungi in the soil. In the roots of the bait platits the parasitic fungus Aphanomyces cochlioides predominated. Rate of infection and yield reduction in the field were decisively influenced by weather conditions. Differences in yield between sugar beet grown in a three-year and a four-year rotation, however, were not significant. An occurrence of beet pests depending on crop rotation was stated only for Atomaria linearis and this only in a few years.  相似文献   
13.
Oral application of a single dose of a new synthetic proteinase inhibitor Camostate (Foy-305) in male Wistar rats was carried out together with studies of in vitro amino acid incorporation followed by separation of proteins by two-dimensional gel electrophoresis. The aim of this experiment was to analyze changes produced by the inhibitor in total protein and individual enzyme biosynthesis. Administration of 100 mg/kg Foy-305 resulted in significant inhibition of total pancreatic protein synthesis, without changes in fractional rates for individual enzymes. 50 mg/kg Foy-305 induced a 10-fold elevation of cholecystokinin (CCK) levels in serum; this persisted for 3 h and led to a significant increase in the total rate of protein synthesis with peak values at 6 and 9 h (78% and 84% above control levels, respectively), returning to control by 15 h. Changes in fractional rates of synthesis occurred with a latency of 6 h and were restricted to amylase and the anionic form of trypsinogen and chymotrypsinogen. Amylase biosynthesis decreased by about 40% from control levels at 9 h to return to control levels by 15 h. Increased synthesis of trypsinogen and chymotrypsinogen was observed; this was also phasic. The results show similar enzyme-specific regulation as previously described for exogenous CCK stimulation and for the adaptation of the pancreas to diets enriched in protein. They demonstrate the effectiveness of pulsatory endogenous hormone release in the regulation of protein synthesis.  相似文献   
14.
Populations of pathogenic Pseudomonas syringae pv. syringae were monitored on apparently healthy leaves, blossoms, and fruit from two apple orchards with known histories of blister bark and a pear orchard with a known history of blossom blast. Populations on blossoms and fruits were higher on pears than on apples. Yellow-pigmented, non-pathogenic bacteria might have suppressed or masked the presence of P. syringae pv. syringae on apple trees. Populations of P. syringae pv. syringae on apple and pear leaves fluctuated sharply but higher levels generally occurred during the 1984/85 growing season than during the drier 1983/84 season. This investigation indicates that the resident phase of P. syringae pv. syringae is probably a major source of inoculum for apple blister bark and pear blossom blast in South Africa.  相似文献   
15.
16.
A mathematical analysis of results from kinetic studies of 125-iododeoxyuridine uptake and loss in almost all the lymphoid and non-lymphoid organs of mice is described. Applied to data gathered from a graft-versus-host reaction experiment, this analysis affords quantitative precision on the differential effects of organ alloantigens on the proliferating grafted cells. It is shown that, depending on the organ and the post-graft period, cell growth can be ascribed to alloantigen-driven cell renewal or to alloantigen-driven trapping or sequestration. Possible applications of the present approach in graft rejection monitoring are discussed.  相似文献   
17.
Summary The epithelial lining of the mucosa of the edentulous, maxillary alveolar ridge was subjected to an ultrastructural and stereological analysis. Four biopsies collected from the non-inflamed crest, i.e., the center over former tooth sockets, in non-denture-wearing female patients 30 to 55 years of age were processed for light and electron microscopy. At the light-microscopic level, epithelial thickness was determined histometrically. Electron micrographs were sampled at two levels of magnification, from five strata in regions of epithelial ridges and from three strata over connective tissue papillae. Standardized stereological pointcounting techniques were employed to analyze a total of 990 electron micrographs. Observations and data revealed that at the alveolar ridge the oral epithelium is truly keratinizing and comprises four strata including a 40±5 m-thick stratum corneum, which displays the oral keratin pattern. The histoand cytodifferentiation were peculiar: (1) Compared to the neighbouring gingival and hard palate epithelium, that of the alveolar crest was markedly thicker, with elongated rete ridges indicating acanthosis. (2) The cytoarchitecture was identical neither to the gingival nor to the hard palate epithelium but revealed a mixture of features typical for either of these two epithelia. Reasons for this are explained on the basis of factors, possible genetic, inherent in epithelial cells that are possibly derived from both the gingival and the palatal environment.  相似文献   
18.
Identification of neurophysin producing cells   总被引:2,自引:0,他引:2  
  相似文献   
19.
A specimen of Ethmorhynchus anophthalmus Meixner 1938 contains a complex of supernumerary genital organs in front of the pharynx. The phenomenon elucidates some traits in the morphogenesis of the atrial organs.
Abkürzungen in den Abbildungen At Atrium genitale - Bu Bursa - Ci Cirrus des Kopulationsorganes - Dc Ductus communis - Ho Hoden - Ke Keimstock - Kop Kopulationsorgan - Ph Pharynx - R Rüssel - Sa Samenblase  相似文献   
20.
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