全文获取类型
收费全文 | 3291篇 |
免费 | 182篇 |
出版年
2021年 | 24篇 |
2020年 | 12篇 |
2019年 | 21篇 |
2018年 | 40篇 |
2017年 | 44篇 |
2016年 | 58篇 |
2015年 | 87篇 |
2014年 | 85篇 |
2013年 | 253篇 |
2012年 | 158篇 |
2011年 | 172篇 |
2010年 | 98篇 |
2009年 | 96篇 |
2008年 | 173篇 |
2007年 | 188篇 |
2006年 | 166篇 |
2005年 | 161篇 |
2004年 | 152篇 |
2003年 | 173篇 |
2002年 | 175篇 |
2001年 | 71篇 |
2000年 | 89篇 |
1999年 | 80篇 |
1998年 | 47篇 |
1997年 | 40篇 |
1996年 | 30篇 |
1995年 | 39篇 |
1994年 | 22篇 |
1993年 | 39篇 |
1992年 | 64篇 |
1991年 | 42篇 |
1990年 | 35篇 |
1989年 | 48篇 |
1988年 | 34篇 |
1987年 | 37篇 |
1986年 | 40篇 |
1985年 | 38篇 |
1984年 | 38篇 |
1983年 | 26篇 |
1982年 | 16篇 |
1981年 | 24篇 |
1980年 | 28篇 |
1979年 | 21篇 |
1978年 | 15篇 |
1977年 | 24篇 |
1976年 | 20篇 |
1975年 | 21篇 |
1974年 | 20篇 |
1973年 | 15篇 |
1972年 | 15篇 |
排序方式: 共有3473条查询结果,搜索用时 15 毫秒
101.
Sachiko Kuno Tetsuo Toraya Suburo Fukui 《Archives of biochemistry and biophysics》1981,210(2):474-480
The apoenzyme of diol dehydrase was inactivated by four sulfhydryl-modifying reagents, p-chloromercuribenzoate, 5,5′-dithiobis(2-nitrobenzoate) (DTNB), iodoacetamide, and N-ethylmaleimide. In each case pseudo-first-order kinetics was observed. p-Chloromercuribenzoate modified two sulfhydryl groups per enzyme molecule and modification of the first one resulted in complete inactivation of the enzyme. DTNB also modified two sulfhydryl groups, but modification of the second one essentially corresponded to the inactivation. In both cases, the inactivation was reversed by incubation with dithiothreitol. Cyanocobalamin, a potent competitive inhibitor of adenosylcobalamin, protected the essential residue, but not the nonessential one, against the modification by these reagents. By resolving the sulfhydryl-modified cyanocobalamin-enzyme complex, the enzyme activity was recovered, irrespective of treatment with dithiothreitol. From these results, we can conclude that diol dehydrase has two reactive sulfhydryl groups, one of which is essential for catalytic activity and located at or in close proximity to the coenzyme binding site. The other is nonessential for activity. Neitherp-chloromercuribenzoate- nor DTNB-modified apoenzyme was able to bind cyanocobalamin, whereas the iodoacetamide- and N-ethylmaleimide-modified apoenzyme only partially lost the ability to bind cyanocobalamin. The inactivation of diol dehydrase by p-chloromercuribenzoate and DTNB did not bring about dissociation of the enzyme into subunits. Total number of the sulfhydryl groups of this enzyme was 14 when determined in the presence of 6 m guanidine hydrochloride. No disulfide bond was detected. 相似文献
102.
Degradation of Xyloglucan by Wall-bound Enzymes from Soybean Tissue I. Occurrence of Xyloglucan-degrading Enzymes in Soybean Cell Wall 总被引:1,自引:0,他引:1
Koyama Toru; Hayashi Takahisa; Kato Yoji; Matsuda Kazuo 《Plant & cell physiology》1981,22(7):1191-1198
An enzyme preparation that catalyzes the degradation of xyloglucanwas obtained by extraction of the cell walls of soybean hypocotylswith a buffer containing 1.0 M NaCl. The enzyme preparationwas shown to catalyze two-step degradation of xyloglucan. Thepolysaccharide was first degraded into comparatively large fragments,which were then further degraded into monosaccharides. In orderto elucidate the mode of degradation of the xyloglucan duringcell growth, the activities of xyloglucandegrading enzymes ofsoybean-hypocotyl segments were assayed at different stagesof elongation. The total activities of the degrading enzymeswere lower in the elongating regions than in the non-elongatingregions. However, high levels of endo-ß-l,4-glucanasewere found in the elongating regions. These results suggestthat xyloglucan is hydrolyzed by endo-ß-1,4-glucanaseinto comparatively large fragments at the initial stage of growthand the resulting fragments are further degraded into monosaccharidesduring cell elongation. (Received May 20, 1981; Accepted August 8, 1981) 相似文献
103.
The accumulation pattern of arachin and its subunits in growinggroundnuts was investigated. Soluble proteins were extractedfrom the kernels at twelve different stages of maturation (416weeks after pegging). Fractionation showed arachin, conarachinII, 5S and 2S protein components with sucrose gradient centrifugation.Ten weeks after pegging, only 35% of the maximum amount of arachinhad accumulated, whereas conarachin II was 85%, the 5S component89%, and the 2S component 76%. Arachin, however, increased rapidlyin the later stage of maturation. No change in the subunit ratioin arachin during seed growth was observed on the patterns ofsodium dodecyl sulfate-gel electrophoresis and gel isoelectricfocusing in the presence of urea. The ratio of the arachin subunitscontained in urea-extractable fraction of the kernels was constantthroughout seed development and was consistent with the subunitratio in arachin. On the other hand, the arachin subunits inthe free forms, if any, accounted for less than 1% of the associatedarachin subunits. Probably, the arachin subunits synthesizedin equimoles are associated into arachin without individualdeposition and are accumulated as arachin associates in growingseeds. (Received July 17, 1980; ) 相似文献
104.
105.
1. The extent of racemization and the coupling yield in peptide synthesis were studied under high dilution conditions. The azide method yielded the best results. 2. Five linear penta-peptide precursors related to gramicidin S were subjected to cyclization in order to study how the difference in the sequence influences the yield and the ratio of cyclic dimer to monomer. The azide with the sequence of -L -Pro-L -Val-L -Orn(Z)-L -Leu-D -Phe- afforded diZ-gramicidin S in a high yield of 63%. 3. Alternaria mali toxin III, a cyclotetradepsipeptide phytotoxin, was synthesized. The activated linear tetradepsipeptide containing a D -Dap(Z) (N3-Z-D -2,3-diaminopropionic acid) residue at the N-terminus afforded the cyclic precursor (53%). The Dap residue in the precursor was converted into a ΔAla residue by Hofmann degradation to give the desired product. 相似文献
106.
A H Koyama T Maeda S Toyama S Ohnishi H Uetake S Toyama 《Biochimica et biophysica acta》1978,508(1):130-136
The nature of the interaction between Sendai virus and Sil mutant cells was examined by measuring a change in ESR spectrum of spin-labeled phosphatidylcholine molecules on the viral envelope. When spin-labeled virus was incubated with the Sil cells that had a reduced ability to respond to virus-induced cell fusion, interchange of the phospholipid molecules between viral envelope and cell surface membrane occurred to a smaller extent than that observed with parental cells. Moreover, the degree of the interchanging correlated with the degree of the fusion capacity of the mutant lines. The results show that the mutant cells carry such a lesion(s) on their surface membranes that the viral envelopes can hardly fuse into them. 相似文献
107.
Tetsuo Koyama 《Brittonia》1978,30(1):102-108
Six Thai species ofFimbristylis, including two new ones, are taxonomically discussed, and some range extensions into Burma are reported. Described as new areFimbristylis kernii from the neighborhood ofF. hookeriana, andF. smitinandii, a clearcut species of the sectionAbildgaardia. 相似文献
108.
109.
Tetsuo Suami Shigeru Nishiyama Yasuhide Ishikawa Shinichi Katsura 《Carbohydrate research》1978,65(1):57-64
The aminocyclitol antibiotic neamine has been modified by changing the configuration of one or two hydroxyl groups of the aminocyclitol moiety to elucidate the relationship between configuration and antimicrobial activity. 5-Epi-, 6-epi-, and 5,6-diepineamine have been prepared and their antimicrobial activity has been determined against several micro-organisms. 相似文献
110.
Tetsuo Suami Shigeru Nishiyama Yasuhide Ishikawa Shinichi Katsura 《Carbohydrate research》1976,52(1):187-196
The aminocyclitol antibiotic neamine has been chemically modified at the hydroxyl group on C-6 of the 2-deoxystreptamine moiety. The partially acetylated neamine derivatives, 6,3′,4′-tri-O-acetyl- (3) and 5,3′,4′-tri-O-acetyl-1,3,2′,6′-tetra-N-(ethoxycarbonyl)neamine (4), were prepared by random hydrolysis of the 5,6-O-ethoxyethylidene derivative (2), followed by chromatographic purification. Condensation of 4 and 2,3,5-tri-O-benzoyl-d-ribofuranosyl chloride led to 6-O-(β-d-ribofuranosyl)neamine (7). Analogous condensation of 4 with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide or 2,3,4,6-tetra-O-acetyl-α-d-galactopyranosyl bromide afforded the corresponding 6-O-(d-hexopyranosyl)neamines. 相似文献