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   6539篇
  免费   470篇
  国内免费   5篇
  2023年   39篇
  2022年   63篇
  2021年   139篇
  2020年   86篇
  2019年   111篇
  2018年   146篇
  2017年   115篇
  2016年   213篇
  2015年   336篇
  2014年   401篇
  2013年   417篇
  2012年   575篇
  2011年   478篇
  2010年   342篇
  2009年   271篇
  2008年   344篇
  2007年   386篇
  2006年   291篇
  2005年   338篇
  2004年   302篇
  2003年   255篇
  2002年   232篇
  2001年   62篇
  2000年   42篇
  1999年   61篇
  1998年   88篇
  1997年   54篇
  1996年   52篇
  1995年   55篇
  1994年   37篇
  1993年   38篇
  1992年   37篇
  1991年   29篇
  1990年   28篇
  1989年   25篇
  1988年   29篇
  1987年   30篇
  1986年   23篇
  1985年   26篇
  1984年   31篇
  1983年   18篇
  1982年   32篇
  1981年   20篇
  1980年   15篇
  1979年   17篇
  1978年   17篇
  1977年   22篇
  1976年   19篇
  1975年   17篇
  1974年   14篇
排序方式: 共有7014条查询结果,搜索用时 15 毫秒
101.
Summary A case of Meckel or Gruber syndrome is reported, together with a survey of the relevant literature of recent years (1971–1977), in reference to a probably autosomal recessive inheritance of this malformation.  相似文献   
102.
The separation of the enantiomers of lactic and glyceric acids can be achieved by capillary gas chromatography on SP-1000 using the corresponding O-acetylated menthyl esters. The structures of the derivatives were proved by proton magnetic resonance spectroscopy and mass spectrometry. The method has been used for the determination of the absolute configurations of lactic and glyceric acids isolated from serum and urine from different patients.  相似文献   
103.
Microbotryum silenes-inflatae (DC) G. Deml & Oberw. and Microbotryum violaceoirregulare (Brandenburger & Schwinn) G. Deml & Oberw., both parasitic in the anthers of Silene vulgaris (Moench) Garcke, are compared by their morphology, karyology, and some cultural characteristics. The infection of their hosts is similar in both species, but causes different sizes of the flowers and different color of the spore mass. The teliospore initials of that smuts are produced in dikaryotic sporogenous hyphae. During gelatinization of the hyphal coat, surface ornamentations on the teliospores are formed. Mature teliospores are monokaryotic, and presumably diploid, reticulate in Microbotryum silenes-inflatae and echinulate in M. violaceo-irregulare. Teliospores of both species germinate without a resting periode. Germination results in a commonly three-celled promycelium, which in M. silenes-inflatae separates from the producing teliospore, while in M. violaceo-irregulare it remains on the teliospore during basidiospore formation. The basidiospores are monokaryotic and propagate by budding. Monokaryotic strains were isolated and characterized by standard yeast identification tests and by some enzymatic activities on solid media. While no differences in the enzymatic activities can be found, the species differ in their utilization of carbon sources.  相似文献   
104.
105.
Electrophoretic variation characterized by the presence (ES-5B+) or absence (ES-5B) of esterase-5B in the plasma of the house mouse has been observed. It is suggested that the expression of esterase-5B is controlled by an autosomal locus, Esr, linked to Ldr-1 on chromosome 6, in addition to the presumptive structural locus Es-5, which is located on chromosome 8. A gene order of Lyt-3-Esr-Ldr-1 was determined by two crosses.Supported by the Deutsche Forschungsgemeinschaft (SFB 46).This is communication No. 33 of a research program devoted to the investigation of cellular distribution and genetics of nonspecific esterases.  相似文献   
106.
Oocyte nuclei of the dipteran insect Heteropeza pygmaea display swift pulsating movements during in vitro follicle formation in the ovaries. Low doses of cytochalasin B (CB) completely inhibit the nuclear movements within a few minutes and cause the nuclei to assume spherical shapes. If the drug is removed, nuclear pulsation is resumed within 5–10 min. Phalloidin and colchicine do not affect the nuclear movements. Actin is shown by indirect immunofluorescence microscopy to be present in considerable amounts all over the cytoplasm of the oocytes. It is concluded that microfilaments are responsible for pulsation of the oocyte nuclei, whereas microtubules are not involved.  相似文献   
107.
108.
Summary A series of new vectors for the model zygomycete Absidia glauca was constructed on the basis of the structural neomycin resistance (Neor) gene controlled by the promoter of the gene for elongation factor 1 (TEF). In order to select for transformed colonies with a stable Neor phenotype, spores from primary transformants were pooled and grown for two sporulation cycles under non-selective conditions. Southern blot analysis of DNA from single spore isolates originating from independent transformant pools allowed the identification of two autonomously replicating plasmids. Retransformation of Escherichia coli and restriction analysis of the two plasmids provided evidence for spontaneous in vivo insertion of a new DNA element (SEG1) from the A. glauca genome. The inserted regions in both plasmids are essentially identical and do not represent repetitive DNA. Compared with other autonomously replicating vectors, these SEG1-containing plasmids are mitotically extremely stable and are passed on to the vegetative spore progeny of a retransformed A. glauca strain. We assume that SEG1 contains structural elements involved in partitioning and stable segregation of plasmids. For the construction of stable transformants of A. glauca, the SEG1 element may be regarded as a major breakthrough, because stabilization of transformed genetic traits by integration is difficult to achieve in all mucoraceous fungi and all known replicating plasmids are mitotically unstable.  相似文献   
109.
PalZ - Hyperostotic fish bones from the presumable Pliocene phosphate-bearing deposits along Lake Manyara, Tanzania, are described. In contrast to marine occurrences of this kind, the pathological...  相似文献   
110.
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