全文获取类型
收费全文 | 2948篇 |
免费 | 136篇 |
国内免费 | 3篇 |
出版年
2021年 | 19篇 |
2019年 | 16篇 |
2018年 | 23篇 |
2017年 | 17篇 |
2016年 | 27篇 |
2015年 | 48篇 |
2014年 | 68篇 |
2013年 | 251篇 |
2012年 | 156篇 |
2011年 | 146篇 |
2010年 | 91篇 |
2009年 | 87篇 |
2008年 | 159篇 |
2007年 | 162篇 |
2006年 | 171篇 |
2005年 | 180篇 |
2004年 | 186篇 |
2003年 | 205篇 |
2002年 | 192篇 |
2001年 | 30篇 |
2000年 | 15篇 |
1999年 | 28篇 |
1998年 | 50篇 |
1997年 | 49篇 |
1996年 | 35篇 |
1995年 | 32篇 |
1994年 | 35篇 |
1993年 | 24篇 |
1992年 | 40篇 |
1991年 | 30篇 |
1990年 | 19篇 |
1989年 | 29篇 |
1988年 | 34篇 |
1987年 | 23篇 |
1986年 | 15篇 |
1985年 | 24篇 |
1984年 | 30篇 |
1983年 | 31篇 |
1982年 | 44篇 |
1981年 | 33篇 |
1980年 | 28篇 |
1979年 | 21篇 |
1978年 | 19篇 |
1977年 | 21篇 |
1976年 | 15篇 |
1975年 | 21篇 |
1974年 | 15篇 |
1973年 | 9篇 |
1971年 | 9篇 |
1970年 | 8篇 |
排序方式: 共有3087条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
35.
36.
Primary production of phytoplankton and secondary production of a daphnid and a chaoborid were studied in a small eutrophic
pond. The gross primary production of phytoplankton was 290 gC m−2 per 9 months during April–December. Regression analysis showed that the gross primary production was related to the incident
solar radiation and the chlorophylla concentration and not to either total phosphorus or total inorganic nitrogen concentration. The mean chlorophylla concentration (14.2 mg m−3), however, was about half the expected value upon phosphorus loading of this pond. The mean zooplankton biomass was 1.60
g dry weight m−2, of whichDaphnia rosea and cyclopoid copepods amounted to 0.69 g dry weight m−2 and 0.61 g dry weight m−2, respectively. The production ofD. rosea was high during May–July and October and the level for the whole 9 months was 22.6 g dry weight m−2.Chaoborus flavicans produced 10 complete and one incomplete cohorts per year. Two consecutive cohorts overlapped during the growing season. The
maximum density, the mean biomass, and the production were 19,100 m−2, 0.81 g dry weight m−2, and 11.7 g dry weight m−2yr−1, respectively. As no fish was present in this pond, the emerging biomass amounted to 69% of larval production. The production
ofC. flavicans larvae was high in comparison with zooplankton production during August–September, when the larvae possibly fed not only
on zooplankton but also algae. 相似文献
37.
A single amino acid substitution in the A subunit of Escherichia coli enterotoxin results in a loss of its toxic activity 总被引:9,自引:0,他引:9
T Tsuji T Inoue A Miyama K Okamoto T Honda T Miwatani 《The Journal of biological chemistry》1990,265(36):22520-22525
A plasmid encoding a mutant gene of heat-labile enterotoxin (LT), produced by enterotoxigenic Escherichia coli, was induced by treatment of plasmid EWD 299 with hydroxylamine. A mutant strain of E. coli HB 101 carrying the mutant plasmid pTUH 6A produced a low toxic LT analogue (mutant LT), which was cross-reactive with anti-LT antibody. The mutant LT activity was less than 0.15 and 0.006% of the normal LT in the rabbit ileal loop test and in the rabbit skin permeability test, respectively. The amino acid composition of the mutant LT-B subunit was the same as that of the normal B subunit. Though the A2 fragment of the mutant LT was identical to normal LT by DNA analysis, the A1 fragment of the mutant LT differed from the normal A1 fragment in one amino acid at position 112; namely it had lysine instead of glutamic acid from the N terminus. These data suggest that glutamic acid at position 112 from the N terminus of the A1 fragment is important for the A subunit to express its biological activity. 相似文献
38.
A mutant hemolysin with lower biological activity produced by a mutant Vibrio parahaemolyticus 总被引:1,自引:0,他引:1
Takeshi Honda Yuxin Ni Schunkichi Hori Hikaru Takakura Susumu Tsunasawa Fumino Sakiyama Toshio Miwatani 《FEMS microbiology letters》1989,61(1-2):95-100
Abstract A mutant toxin (m-TDH) of thermostable direct hemolysin (Vp-TDH) of Vibrio parahaemolyticus w was isolated from the culture of a strain of this organism mutagenized with N -methyl- N '-nitro- N -nitrosoguanidine. Although the m-TDH had a molecular structure similar to the native Vp-TDH, the m-TDH retained only about 7% residual hemolytic activity of the native toxin. Furthermore, other biological activities of m-TDH, such as lethality in mice and enterotoxicity in rabbit ileal loops, were also weakened. The m-TDH was immunologically indistinguishable from the native Vp-TDH. These results suggest that the m-TDH is only slightly different in structure from the native Vp-TDH. Also, the mutagenized site in m-TDH, which is not immunogenic, seems to be involved in expressing not only hemolytic activity but also lethal and enterotoxic activity. 相似文献
39.
Masafumi Kuzuya Shosuke Satake Hisayuki Miura Toshio Hayashi Akihisa Iguchi 《Experimental cell research》1996,226(2):336
The vascular basement membrane is involved in the regulation of endothelial cell differentiation. The accumulation of advanced glycosylation endproducts (AGEs) has been demonstrated on these basement membranes in patients with diabetes. We examined the effect of AGEs on endothelial cell behavior on reconstituted basement membrane, Matrigel. Human umbilical vein-derived endothelial cells (HUVECs) stopped proliferating and differentiated into capillary-like tube-shaped structures on Matrigel. Laminin antibody partially blocked this process. HUVECs cultured on glycosylated Matrigel, however, proliferated and formed a monolayer without tube formation. The inclusion of aminoguanidine, an inhibitor of AGE formation, during the glycosylation of Matrigel restored HUVEC differentiation. Although the laminin adsorbed onto the plastic culture wells promoted HUVEC attachment and spreading, glycosylated laminin reduced HUVEC attachment by 50% and abolished cellular spreading. These effects were restored by aminoguanidine. HUVEC attachment to glycosylated laminin was further reduced by AGE-modified albumin, poly I, acetylated low-density lipoprotein, or maleylated albumin, ligands for a scavenger receptor. Coating the culture dishes with the laminin peptides RGD, YIGSR, and SIKVAV supported the attachment of HUVECs that was unaffected by glycosylation. Results suggest that AGE accumulation on the basement membranes inhibits endothelial cell differentiation by impairing the normal interactions of endothelial cell receptors with their specific matrix ligands. This process may be involved in diabetic angiopathy. 相似文献
40.
Hiroyuki Tsunoda Toshio Ohshima Jun Tohyama Masayuki Sasaki Norio Sakuragawa Frank Martiniuk 《Human genetics》1996,97(4):496-499
We report a missense mutation in an adult Japanese patient with acid alpha-glucosidase (GAA) deficiency. A TC to GT transition
at nucleotides 1585–1586, was identified. This transition resulted in an amino acid substitution of Ser-529 to Val (S529V)
in exon 11. We also have demonstrated that the S529V mutation abolishes the catalytic activity of the enzyme. Our data suggest
that this mutation is the cause of the clinical manifestation known as adult-onset GAA deficiency. The missense mutation described
here is a new mutation, and the first identified in Japanese patients with GAA deficiency.
Received: 23 May 1995 相似文献