全文获取类型
收费全文 | 40824篇 |
免费 | 4375篇 |
国内免费 | 12篇 |
出版年
2022年 | 274篇 |
2021年 | 526篇 |
2020年 | 350篇 |
2019年 | 429篇 |
2018年 | 553篇 |
2017年 | 518篇 |
2016年 | 907篇 |
2015年 | 1625篇 |
2014年 | 1590篇 |
2013年 | 2102篇 |
2012年 | 2403篇 |
2011年 | 2111篇 |
2010年 | 1467篇 |
2009年 | 1325篇 |
2008年 | 1836篇 |
2007年 | 1811篇 |
2006年 | 1615篇 |
2005年 | 1590篇 |
2004年 | 1489篇 |
2003年 | 1296篇 |
2002年 | 1283篇 |
2001年 | 1240篇 |
2000年 | 1244篇 |
1999年 | 1110篇 |
1998年 | 611篇 |
1997年 | 565篇 |
1996年 | 564篇 |
1995年 | 541篇 |
1994年 | 497篇 |
1993年 | 517篇 |
1992年 | 1019篇 |
1991年 | 759篇 |
1990年 | 777篇 |
1989年 | 763篇 |
1988年 | 662篇 |
1987年 | 601篇 |
1986年 | 615篇 |
1985年 | 716篇 |
1984年 | 551篇 |
1983年 | 420篇 |
1982年 | 346篇 |
1981年 | 314篇 |
1980年 | 257篇 |
1979年 | 382篇 |
1978年 | 349篇 |
1977年 | 243篇 |
1976年 | 229篇 |
1975年 | 201篇 |
1974年 | 291篇 |
1973年 | 251篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
The Wageningen Delivery of Functionality symposium covered all aspects involved with food structural design to arrive at high-quality
foods which meet demanding customer expectations and regulatory requirements. The symposium integrated aspects from the structural
organization of foods at molecular and supramolecular scales to dedicated techniques required to describe and visualize such
structures, the gastro-intestinal events and how to model these in a laboratory setting, and finally the impact those food
structures and ingredients have on the consumer’s physiology and on the human perception. As an interdisciplinary platform,
bringing together more than 160 researchers from academia and industry, the symposium meanwhile fulfills an important role
in the food science community. 相似文献
22.
Two-dimensional crystallization of bovine rhodopsin 总被引:1,自引:0,他引:1
E A Dratz J F Van Breemen K M Kamps W Keegstra E F Van Bruggen 《Biochimica et biophysica acta》1985,832(3):337-342
Bovine rhodopsin has been clustered into two-dimensional crystals in highly purified native rod disk membranes and studied with negative staining and transmission electron microscopy. The lattice is P2(1) with dimensions of 8.3 X 7.9 nm and interaxis angles of 86 +/- 3 degrees. 110 images of ordered areas were digitized and aligned with computer-correlation methods to calculate an average image with diffraction to the fourth order. The images were computer-filtered and reconstructed to approx. 2 nm resolution. When crystals appeared they covered 20-40% of the surface of the preparation and, since rhodopsin is at least 95% of the protein, there is no doubt that the crystals were due to rhodopsin. There appear to be two rhodopsin dimers per unit cell. Each rhodopsin molecules takes up about 7.5 nm2 of membrane area and is estimated to be associated with about 12 lipids on each side of the membrane. The membrane area found for bovine rhodopsin supports the rhodopsin origin of rarely seen but more highly ordered two-dimensional crystals found in detergent-treated frog rod membranes (Corless, J.M., McCaslin, D.R. and Scott, B.L. (1982) Proc. Natl. Acad. Sci. USA 79, 1116-1120). Furthermore, the rhodopsin membrane area is close to that of bacteriorhodopsin and is consistent with a seven transmembrane helix structure proposed for rhodopsin (for references see Dratz, E.A. and Hargrave, D.A. (1983) Trends Biochem. Sci. 8, 128-131). Crystallization was accomplished by lowering the pH to 5.5 near the isoelectric point of rhodopsin, raising the salt concentration of 2 M (NH4)2SO4, adding 5% glucose and 0.02% Hibitane (Ayerst), a cationic amphipathic antiseptic that favored crystal growth. 相似文献
23.
Nitracrine is used clinically as an antitumour agent, and analogues are actively being developed in some laboratories. The mutagenic activity of 9-[(3-dimethylaminopropyl)amino]-acridine and its 1-nitro (nitracrine), 2-, 3- and 4-nitro derivatives was evaluated at the 6-thioguanine and ouabain resistance loci in cultured Chinese hamster fibroblasts (V79-171b cell line). The des-nitro, 2- and 3-nitro caused no statistically significant mutagenic activity at either locus. Each of these 3 compounds weakly increased (approximately 2-fold) the incidence of micronuclei in the same cell line when tested at cytotoxic doses. Both the 1- and 4-nitro compounds increased the incidence of 6-thioguanine resistant cells from around 1 in 10(-6) to approximately 1 in 10(-4). The former compound significantly increased the frequency of ouabain-resistant cells. Both of these compounds were potent inducers of micronuclei in V79-171b cells, indicating high clastogenic activity. It would appear prudent to regard both of these compounds as potential human carcinogens. 相似文献
24.
F. D. Miller K. F. Jorgenson R. J. Winkfein J. H. van de Sande D. A. Zarling J. Stockton 《Journal of biomolecular structure & dynamics》2013,31(3):611-620
Abstract Bacteriophage PM2 DNA, a ccc genome of high apparent superhelical density, contains left-handed (Z) regions as detected by competitive radioimmunoassay, agarose gel electrophoresis of DNA: antibody complexes and immunoelectron microscopy. The latter technique, in conjunction with partial blockage of restriction endonuclease sites by bound antibody, was used to map the left-handed regions along the DNA molecule. A cluster of four to five antibody molecules (approximately 25% of bound antibody) was located within map units 0.05–0.18 of the single Hpa II restriction site. Sequence analysis of part of this region showed the presence of several areas of high alternating purine-pyrimidine content. A strong correlation is observed between alternating pyrimidine-purine tracts of significant length and antibody binding sites. 相似文献
25.
26.
J. A. Roubos C. D. de Gooijer G. van Straten A. J. B. van Boxtel 《Bioprocess and biosystems engineering》1997,17(2):99-102
Two methods for the calculation of optimal trajectories for the input variables of a fed-batch culture of hybridoma cells are compared. It pointed out that a gradient method based on Pontryagins' minimum principle based yields a significant better performance with respect to computational effort and the calculated minimum than a dynamic programming approach which has been presented in a previous paper [1] as the most suitable method. 相似文献
27.
M Lebl E E Sugg G van Binst P Vander Elst D Tourwé J Slaninová V J Hruby 《International journal of peptide and protein research》1987,30(3):318-322
Analogs of deamino-oxytocin and deamino-oxypressin containing a CH2-NH group instead of an amide bond between positions 8 and 9 were synthesized. All tested compounds exhibit significantly lowered biological activities. 相似文献
28.
29.