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   2793篇
  免费   226篇
  国内免费   1篇
  2021年   26篇
  2020年   32篇
  2019年   35篇
  2018年   37篇
  2017年   36篇
  2016年   42篇
  2015年   82篇
  2014年   91篇
  2013年   113篇
  2012年   137篇
  2011年   101篇
  2010年   88篇
  2009年   79篇
  2008年   100篇
  2007年   101篇
  2006年   110篇
  2005年   113篇
  2004年   110篇
  2003年   126篇
  2002年   112篇
  2001年   42篇
  2000年   72篇
  1999年   53篇
  1998年   39篇
  1997年   27篇
  1996年   27篇
  1995年   34篇
  1994年   25篇
  1993年   35篇
  1992年   38篇
  1991年   41篇
  1990年   44篇
  1989年   41篇
  1988年   38篇
  1987年   30篇
  1986年   36篇
  1985年   41篇
  1984年   45篇
  1983年   33篇
  1982年   30篇
  1980年   23篇
  1979年   36篇
  1977年   28篇
  1976年   34篇
  1974年   34篇
  1973年   26篇
  1972年   24篇
  1970年   27篇
  1969年   22篇
  1968年   23篇
排序方式: 共有3020条查询结果,搜索用时 734 毫秒
1.
Abstract. Although the oesophageal appendages in the four enchytraeids Enchytrueus crypticus, Fredericia strinta, Buchholzia appendiculata , and Achaeta sp. are quite different from one another in shape and position, their histology and ultrastructure are basically the same. These are intestinal appendages, the lumina of which distally end blind and proximally open into the oesophagus. Almost all of the few cells in their single-layered epithelium have a microvillous, cilia-free border at the apex, facing towards the lumen, and basally comprise an extremely extensive labyrinth. The presence of the latter, composed of very thin cell processes, and of numerous mitochondria identifies the organs as energy-producing and -consuming, transport-active structures. Their possible function as a food-moistening organ or osmoregulatory organ is discussed, and they are compared with other intestinal appendages in enchytraeids and other oligochaetes.  相似文献   
2.
3.
The polar lipids of the autotrophically grown, obligately anaerobic, photosynthetic bacterium Chromatium strain D were separated by paper chromatography. Four major phospholipids were identified: lysophosphatidylethanolamine, phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin. In addition, three glycolipids were observed and characterized, namely, monoglucosyldiglyceride, which is found in other biological systems, and (mannosyl, glucosyl)-diglyceride and (dimannosyl, glucosyl)-diglyceride, which heretofore have not been observed in nature.  相似文献   
4.
5.
Besprechungen     
Ohne Zusammenfassung  相似文献   
6.
7.
Ohne ZusammenfassungMit 7 Textabbildungen.In ausführlicherer Form und mit zahlreichen Abbildungen als Dissertation bei der Naturwissenschaftlichen Fakultät der Universität München eingereicht.  相似文献   
8.
Abstract. The pupal stage of ten Coelometopini species occurring in Australia, New Guinea, Southeast Asia and the Pacific region are described and a key for their identification is provided. The species are Chrysopeplus expolitus Broun, Derosphaerus hirtipes Kaszab, Hypaulax crenata (Boisduval), Leprocaulus borneensis Kaszab, Metisopus purpureipennis Bates, Promethis carteri Kaszab, P. nigra (Blessig), P. quadraticollis (Gebien), P. quadricollis Pascoe and P. sulcigera (Boisduval). The gin trap structures of D. hirtipes and P. quadraticollis are described in detail using scanning electron micrographs. A summary of antipredator structures of all known Coelometopini pupae is given. The phylogenetic value of pupal characters is assessed at intra‐ and intergeneric levels within the tribe.  相似文献   
9.
Summary The feasibility of cellulase production by Trichoderma reesei using inexpensive lignocellulosic material was examined. Sulfite pulp used as standard substrate yielded 3.7 IU/ml filter paper units (FPU) and 2.15 IU/ml -glucosidase. The yield was 185 FPU per gram total carbohydrate (CH) in the fermentation medium. Steam treated wheat straw (2%) gave 1.9 FPU/ml, 0.83 IU/ml -glucosidase and 151 FPU/g CH, whereas the spent fibres remaining after enzymatic hydrolysis of steamed wheat straw gave 2.4 FPU/ml, 1.55 IU/ml -glucosidase and 147 FPU/g CH. A good substrate (3%) was also the combustible fraction of municipal waste (BRAM) treated with NaOH, which gave 2.5 FPU/ml, 0.86 IU/ml -glucosidase and 130 FPU/g CH. A further increase in the final enzyme titer is obtainable by increasing the substrate concentration. In shake cultures 5% steamed wheat straw gave 3.8 FPU/ml and 1.95 IU/ml -glucosidase. Untreated wheat straw gave only low final enzyme titers and low yields of FPU/g CH. In the case of lignocellulosic substrates a constant pH-value of pH 6.0 during the fermentation gave optimal yields.  相似文献   
10.
Summary Fractionation of rabbit skeletal muscle cytosol on Aminohexyl-Sepharose has resulted in the identification of a latent ATP, Mg-dependent protein phosphatase whose catalytic subunit is in the active conformation, but is inhibited by the presence of more than one modulator unit. The partially purified enzyme is converted to an inactive, kinase FA-dependent form upon incubation at 30°C unless modulator-specific polyclonal antibodies are added to the preparation. The immunoglobulins also relieve the inhibition which is responsible for the low basal phosphatase activity of the enzyme, and they counteract all of the heat-stable inhibitor activity present in the preparation. Addition of free catalytic subunit abolishes the inhibition of the latent enzyme in a dose-dependent way, but cannot prevent the inactivation process. The inactivated phosphatase and the original latent enzyme exhibit the same apparent M r in sucrose density-gradient centrifugation (70 000) and in gel filtration (110 000).Abbreviations PMSF Phenylmethanesulphonyl Fluoride - TLCK L-l-chloro-3-(4-tosylamido)-7-amino2-heptanone-hydrochloride - TPCK L-l-chloro-3-(4-tosvlamido)-4-phenyl-2-butanone  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