全文获取类型
收费全文 | 3423篇 |
免费 | 241篇 |
出版年
2022年 | 19篇 |
2021年 | 28篇 |
2020年 | 24篇 |
2019年 | 19篇 |
2018年 | 39篇 |
2017年 | 41篇 |
2016年 | 46篇 |
2015年 | 72篇 |
2014年 | 86篇 |
2013年 | 198篇 |
2012年 | 136篇 |
2011年 | 142篇 |
2010年 | 104篇 |
2009年 | 103篇 |
2008年 | 172篇 |
2007年 | 163篇 |
2006年 | 179篇 |
2005年 | 183篇 |
2004年 | 179篇 |
2003年 | 179篇 |
2002年 | 194篇 |
2001年 | 92篇 |
2000年 | 90篇 |
1999年 | 110篇 |
1998年 | 50篇 |
1997年 | 50篇 |
1996年 | 41篇 |
1995年 | 41篇 |
1994年 | 50篇 |
1993年 | 41篇 |
1992年 | 82篇 |
1991年 | 52篇 |
1990年 | 64篇 |
1989年 | 60篇 |
1988年 | 38篇 |
1987年 | 44篇 |
1986年 | 42篇 |
1985年 | 41篇 |
1984年 | 46篇 |
1983年 | 30篇 |
1982年 | 31篇 |
1981年 | 23篇 |
1980年 | 16篇 |
1979年 | 24篇 |
1978年 | 24篇 |
1977年 | 26篇 |
1976年 | 20篇 |
1975年 | 21篇 |
1974年 | 18篇 |
1970年 | 14篇 |
排序方式: 共有3664条查询结果,搜索用时 15 毫秒
1.
We have previously shown that replacing the P1-site residue (Ala) of chicken ovomucoid domain 3 (OMCHI3) with a Met or Lys results in the acquisition of inhibitory activity toward chymotrypsin or trypsin, respectively. However, the inhibitory activities thus induced are not strong. In the present study, we introduced additional amino acid replacements around the reactive site to try to make the P1-site mutants more effective inhibitors of chymotrypsin or trypsin. The amino acid replacement Asp-->Tyr at the P2' site of OMCHI3(P1Met) resulted in conversion to a 35000-fold more effective inhibitor of chymotrypsin with an inhibitor constant (K(i)) of 1. 17x10(-11) M. The K(i) value of OMCHI3(P1Met, P2'Ala) indicated that the effect on the interaction with chymotrypsin of removing a negative charge from the P2' site was greater than that of introducing an aromatic ring. Similarly, enhanced inhibition of trypsin was observed when the Asp-->Tyr replacement was introduced into the P2' site of OMCHI3(P1Lys). Two additional replacements, Asp-->Ala at the P4 site and Arg-->Ala at the P3' site, made the mutant a more effective inhibitor of trypsin with a K(i) value of 1. 44x10(-9) M. By contrast, Arg-->Ala replacement at the P3' site of OMCHI3(P1Met, P2'Tyr) resulted in a greatly reduced inhibition of chymotrypsin, and Asp-->Ala replacement at the P4 site produced only a small change when compared with a natural variant of OMCHI3. These results clearly indicate that not only the P1-site residue but also the characteristics, particularly the electrostatic properties, of the amino acid residues around the reactive site of the protease inhibitor determine the strength of its interactions with proteases. Furthermore, amino acids with different characteristics are required around the reactive site for strong inhibition of chymotrypsin and trypsin. 相似文献
2.
Masami Takagi 《Oecologia》1985,68(1):1-6
Summary
Pteromalus puparum is a gregarious parasitoid of many butterfly pupae. Adult size, mortality, and sex ratio of P. puparum, as a parasitoid of Papilio xuthus, were unit weight of the host. Effects of female size on fecundity, wing load, and longevity were also examined.The highest total weight of progeny from the host was attained when the number of eggs per gram of the host was approximately 150. Positive correlations were observed between the size of the females and their fecundity and wing load. The maximum longevity of the female kept with honey but without hosts was attained when the initial number of parasitoids per g of the host was 150.Considering the total fecundity of all female progeny, the reproductively most efficient number of eggs to be deposited per g of the host was estimated to be approximately 300. However, as shortage of food for the adult females strongly affects their fecundity, the reproductively most efficient number of eggs to be deposited per g of the host was about 70 when the adult female progeny was not provided with food.The optimal number of eggs to be deposited when the emale oviposits in the host under field conditions is discussed. 相似文献
3.
We examined whether actin filaments are involved in the cAMP-dependent activation of a high affinity sodium/glucose cotransporter (SGLT1) using epithelial expression systems. The expression of enhanced green fluorescent protein-tagged SGLT1 (EGFP-SGLT1) in Madin-Darby canine kidney (MDCK) cells was revealed by Western blotting and confocal laser microscopy. 8-Br-cAMP, a membrane permeable cAMP analog, enhanced [14C]-α-methyl glucopyranoside ([14C]-AMG) uptake. Both basal and 8-Br-cAMP-elicited [14C]-AMG uptakes were inhibited by N-(2{[3-(4-bromophenyl)-2-propenyl]-amino}-ethyl)-5-isoquinolinesulfonamide (H-89), a protein kinase A inhibitor, and cytochalasin D, an actin filament formation inhibitor. Furthermore, cytochalasin D inhibited the distribution of EGFP-SGLT1 at the apical surface. These results suggest that the EGFP-SGLT1 protein is functionally expressed in the apical membrane of MDCK cells, and is up-regulated by a cAMP-dependent pathway requiring intact actin filaments. 相似文献
4.
A case of chromomycosis in which hyperthermia proved effective is reported. The patient was a 56-year-old male bean curd maker who, without any previous history of minor trauma, developed on the extensor side of the left upper arm an eczematous lesion that underwent gradual radial expansion. The lesion showed a well-defined, 7×10 cm infiltrated erythematous plaque with the central area healed and, at the upper and lower borders, adherent scales and crusts on the surface. Histological examination revealed granulomatous changes in the dermis, as well as sclerotic cells within giant cells and microabscesses. On culturing,Fonsecaea pedrosoi was isolated. The patient was treated with disposable chemical pocket warmers, which were secured over the lesion with a rather tight elastic bandage, so that they kept the affected area warm for 24 hours a day. After a month of such hyperthermic treatment, the erythema and infiltration had decreased considerably, and microscopic examination and culture of the crusts both yielded negative results. Examination of biopsy specimens of the lesion after the third month showed that it had cicatrized. The treatment was stopped after 4 months, and no relapse occurred. We also summarize the published results of local hyperthermic treatment of chromomycosis in Japan. 相似文献
5.
6.
7.
In designing new DNA recognizing and cleaving reagents, we introduce herein a bisacridine derivative (referred to as bisacridine) in which two acridine heterocycles are connected by a penta(ethylene glycol) bridging chain. This compound offers two possible functions: 1, stabilization of DNA bisacridine intercalator complex by metal ion. The penta(ethylene glycol) chain stabilizes metal ions binding to the phosphate site of DNA, where the penta(ethylene glycol) chain constitutes a part of a pseudomacrocyclic ligand for metal binding; and 2, enhancement of metal-assisted hydrolytic cleavage of DNA by means of a metal concentration effect by the pseudomacrocyclic ethereal chain. The binding isotherms of bisacridine with DNA in the presence of metal ions showed that the binding was mainly governed by the cation exchange reaction on the anionic DNA polymer chain, i.e., the exchange between metal ions and the cationic bisacridine. The bisacridine showed an increase DNA binding ability compared to quinacrine, the monoacridine counterpart, and caused an enhancement of DNA cleavage in the presence of Cu2+ ions. Additional experiments which included DNase 1 footprinting in the presence of bisacridine and the DNA cleavage by Cu2+/bisacridine using a 32P end-labelled DNA fragment, suggested that the Cu2(+)-assisted DNA cleavage sites in the presence of bisacridine were in reasonable overlap with the DNA binding sites of bisacridine. 相似文献
8.
Barbara Tillmann Pierre Jolic?ur Masami Ishihara Nathalie Gosselin Olivier Bertrand Yves Rossetti Isabelle Peretz 《PloS one》2010,5(4)
Congenital amusia is a neurogenetic disorder of music processing that is currently ascribed to a deficit in pitch processing. A recent study challenges this view and claims the disorder might arise as a consequence of a general spatial-processing deficit. Here, we assessed spatial processing abilities in two independent samples of individuals with congenital amusia by using line bisection tasks (Experiment 1) and a mental rotation task (Experiment 2). Both amusics and controls showed the classical spatial effects on bisection performance and on mental rotation performance, and amusics and controls did not differ from each other. These results indicate that the neurocognitive impairment of congenital amusia does not affect the processing of space. 相似文献
9.
Norio Masui Yumie Takagi Tetsu Nishikawa Makoto Yanabe Masato Nose Katsunori Sato 《Experimental Animals》2002,51(5):501-503
A new polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis was developed for genetic typing of the mouse Tnfsf6gld mutation. An artificial restriction site was introduced to the mouse Tnfsf6gld mutation by PCR amplification using a modified primer. The three genotypes of the Tnfsf6 locus (Tnfsf6gld/Tnfsf6gld, Tnfsf6gld/+, and +Tnfsf6-gld/+Tnfsf6-gld) could be distinguished clearly and easily. This PCR-RFLP analysis was found to be useful for the identification of the mouse Tnfsf6gld mutation. 相似文献
10.