全文获取类型
收费全文 | 17845篇 |
免费 | 1835篇 |
国内免费 | 2686篇 |
专业分类
22366篇 |
出版年
2024年 | 88篇 |
2023年 | 420篇 |
2022年 | 514篇 |
2021年 | 638篇 |
2020年 | 727篇 |
2019年 | 878篇 |
2018年 | 751篇 |
2017年 | 752篇 |
2016年 | 770篇 |
2015年 | 695篇 |
2014年 | 845篇 |
2013年 | 1259篇 |
2012年 | 791篇 |
2011年 | 797篇 |
2010年 | 617篇 |
2009年 | 803篇 |
2008年 | 770篇 |
2007年 | 873篇 |
2006年 | 805篇 |
2005年 | 755篇 |
2004年 | 628篇 |
2003年 | 609篇 |
2002年 | 575篇 |
2001年 | 455篇 |
2000年 | 416篇 |
1999年 | 403篇 |
1998年 | 331篇 |
1997年 | 295篇 |
1996年 | 350篇 |
1995年 | 316篇 |
1994年 | 308篇 |
1993年 | 257篇 |
1992年 | 208篇 |
1991年 | 261篇 |
1990年 | 192篇 |
1989年 | 194篇 |
1988年 | 156篇 |
1987年 | 167篇 |
1986年 | 149篇 |
1985年 | 185篇 |
1984年 | 202篇 |
1983年 | 138篇 |
1982年 | 188篇 |
1981年 | 129篇 |
1980年 | 151篇 |
1979年 | 112篇 |
1978年 | 86篇 |
1977年 | 81篇 |
1976年 | 74篇 |
1975年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
J.G. Roddick 《Phytochemistry》1974,13(1):9-25
The literature relating to chemical, biochemical and biological aspects of the steroidal glycoalkaloid, α-tomatine, is reviewed. The alkaloid, which can be used as a starting compound for the synthesis of steroidal hormones, is toxic to a wide range of living organisms. The significance of tomatine to plants which elaborate it is discussed and some possible uses of the compound are mentioned. 相似文献
2.
The ability to metabolically label proteins with 35S-methionine is critical for the analysis of protein synthesis and turnover. Despite the importance of this approach, however, efficient labeling of proteins in vivo is often limited by a low number of available methionine residues, or by deleterious side-effects associated with protein overexpression. To overcome these limitations, we have created a methionine-rich variant of the widely used HA tag, called HAM, for use with ectopically expressed proteins. Here we describe the development of a series of vectors, and corresponding antisera, for the expression and detection of HAM-tagged proteins in mammalian cells. We show that the HAM tag dramatically improves the sensitivity of 35S-methionine labeling, and permits the analysis of Myc oncoprotein turnover even when HAM-tagged Myc is expressed at levels comparable to that of the endogenous protein. Because of the improved sensitivity provided by the HAM tag, the vectors and antisera described here should be useful for the analysis of protein synthesis and destruction at physiological levels of protein expression. 相似文献
3.
Samples of marine pleuston were collected from the sea-surface along considerable sections of the track of Eye of the Wind during its 2-year circumnavigational expedition 'Operation Drake' from November 1978 to October 1980. One hundred and eleven of the tow samples contained insects of the genus Halobates . They were assigned to four oceanic species: H. micans, H. sericeus, H. germanus and H. splendens; two coastal species: H. maculatus, H. princeps, and one undescribed species. Various development stages of the oceanic species were found. The locations, time of collection and surface temperatures where sea-skaters were collected are tabulated. Distributional boundaries and population densities of the oceanic species collected are discussed. 相似文献
4.
John H. Pazur Belin Liu Steven Pyke Craig R. Baumrucker 《Journal of Protein Chemistry》1987,6(6):517-527
Glucoamylase is a starch-hydrolyzing enzyme with a glycoprotein structure, used industrially for the conversion of starch to glucose, citric acid, corn syrups, and high-fructose sweeteners. This enzyme possesses an unusual type of structure in which many carbohydrate side chains are linked O-glycosidically to serine and threonine residues of the polypeptide chain. The carbohydrate side chains may be single monosaccharide residues or oligosaccharides of mannose, glucose, galactose, and in some cases N-acetylglucosamine. New data from experiments on the CNBr fragmentation of glucoamylase followed by chemical and immunological characterization of the fragments show that the carbohydrate side chains are distributed randomly along the polypeptide chain. Such a structure is appropriately termed a random model reprensentation for the glucoamylase molecule. 相似文献
5.
R Liang 《Biochemical and biophysical research communications》1984,120(3):741-746
Primary cell cultures were prepared from breast muscles of 11 day 4 hour-embryonic chicks. Cytoplasmic RNAs were isolated from the cultured cells at various time intervals from day 3 to day 8. A [P32] DNA probe complementary to messenger RNA of myosin heavy chain was used to hybridize with the RNAs after gel electrophoresis. A transient species of polyadenylated RNA with a decreased mobility in electrophoresis was detected during a period of time when contractions of syncytial fibers were first observed. 相似文献
6.
Three species of blackflies were found in emergence-trap samples taken overa period of 8 months from a second-order, forested, cold-stenothermal stream in southern Ontario. The emergence phenologies of the two common species, Prosimulium mixtum and Stegopterna mutata, are described and compared with their phenologies in other streams in North America. Hypotheses are presented for the poor faunal diversity and prolonged emergence of the two species in the stream studied. Emergence data are used to describe the pupal distribution in the stream.Wing-length measurements showed a distinct dimorphism in P. mixtum: females were larger than males. Adult size (except of P. mixtum females) varied among sampling sites in the stream and, in the case of S. mutata, this variation was time dependent. 相似文献
7.
8.
9.
J. L. Wilkens T. Kuramoto 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(7):483-490
The decapod cardiovascular system consists of a single ventricle that pumps blood into seven arteries; previous work has
shown that the outflow distribution patterns of intact animals are variable. In the present study, flow recordings were made
from pairs of arteries in semi-isolated hearts whilst different cardioactive hormones were infused into the heart. Each hormone
(5-hydroxytryptamine, octopamine, dopamine, proctolin and F1) changed the outflow pattern, heart rate and ventricular pressure
in a unique way. The probable sites of hormone action are the cardioarterial valves located at the origin of each artery except
one, the dorsal abdominal. Outflow from the dorsal abdominal is controlled downstream by valves located at the origin of the
segmental lateral arteries. The responses to a particular hormone were sometimes different between the hearts of American
and Japanese lobsters.
Accepted: 11 May 1998 相似文献
10.