全文获取类型
收费全文 | 12705篇 |
免费 | 1038篇 |
国内免费 | 9篇 |
出版年
2023年 | 51篇 |
2022年 | 98篇 |
2021年 | 234篇 |
2020年 | 134篇 |
2019年 | 201篇 |
2018年 | 238篇 |
2017年 | 218篇 |
2016年 | 315篇 |
2015年 | 608篇 |
2014年 | 638篇 |
2013年 | 775篇 |
2012年 | 1061篇 |
2011年 | 1015篇 |
2010年 | 637篇 |
2009年 | 582篇 |
2008年 | 825篇 |
2007年 | 846篇 |
2006年 | 725篇 |
2005年 | 724篇 |
2004年 | 684篇 |
2003年 | 638篇 |
2002年 | 641篇 |
2001年 | 122篇 |
2000年 | 85篇 |
1999年 | 134篇 |
1998年 | 155篇 |
1997年 | 127篇 |
1996年 | 113篇 |
1995年 | 115篇 |
1994年 | 99篇 |
1993年 | 75篇 |
1992年 | 88篇 |
1991年 | 57篇 |
1990年 | 60篇 |
1989年 | 61篇 |
1988年 | 34篇 |
1987年 | 36篇 |
1986年 | 41篇 |
1985年 | 40篇 |
1984年 | 49篇 |
1983年 | 36篇 |
1982年 | 59篇 |
1981年 | 39篇 |
1980年 | 43篇 |
1979年 | 27篇 |
1978年 | 31篇 |
1977年 | 33篇 |
1976年 | 18篇 |
1975年 | 18篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
We previously demonstrated inhibition of Na+-dependent 32Pi transport in canine renal brush-border membranes in association with NAD+-induced ADP ribosylation of membrane protein(s) and postulated that NAD+ inhibits Pi transport across the brush-border membrane via ADP ribosylation. Recently it was shown that incubation of rat brush-border membrane with NAD+ resulted in release of Pi which was prevented by EDTA. It was proposed that NAD+-mediated inhibition of 32Pi transport might occur through this mechanism. To determine whether NAD+ inhibited 32Pi transport by a mechanism other than or in addition to release of Pi, we compared Na+-dependent 32Pi counterflow in brush-border membrane equilibrated with Pi or with Pi generated from NAD+. Release of Pi from NAD+ incubated with brush-border membrane was confirmed. The increased uptake of 32Pi which was demonstrated in brush-border membrane equilibrated with Pi was not measured when intravesicular Pi was generated from a concentration of NAD+ which effected ADP-ribosylation of brush border membranes (100 μM NAD+). In contrast, increased uptake of 32Pi was demonstrated when intravesicular Pi was generated from 1 μM NAD+ which did not effect ADP ribosylation. Mg2+-dependent ADP ribosylation of brush-border membrane incubated with NAD+ was demonstrated which persisted during the time interval of 32Pi uptake measurements. Our findings are compatible with the hypothesis that NAD+-induced ADP ribosylation of brush-border membrane protein(s) results in inhibition of Pi transport across the membrane in vivo. EDTA may act to prevent this inhibition in brush-border membrane by chelation of Mg2+ and decreased ADP ribosylation. 相似文献
52.
Mavis Hendson Lizzie Askjaer Jennifer A. Thomson Marc van Montagu 《Applied microbiology》1983,45(5):1526-1532
Eighteen strains of Agrobacterium tumefaciens isolated from crown galls were tested for agrocin production. Of six agrocin-producing strains, one (D286) produced a broad-host-range agrocin active against strains carrying nopaline, octopine, and agropine type Ti plasmids. Sensitivity to agrocin D286 was found to map in the 11- to 18-megadalton region of the nopaline Ti plasmid pTiC58. The agrocin was partially purified, and its physical characteristics were consistent with its being a nucleotide, as is agrocin 84. Agrocin D286 was shown to inhibit DNA, RNA, and protein syntheses. Strain D286 spontaneously lost its pathogenicity, and its potential for use in the biological control of crown gall is discussed. 相似文献
53.
Intracellular folate distribution in cultured fibroblasts from patients with the fragile X syndrome. 总被引:1,自引:1,他引:0
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
B W Popovich D S Rosenblatt B A Cooper M Vekemans 《American journal of human genetics》1983,35(5):869-878
Altered folate metabolism has been suggested as a possible reason for expression of the fragile X chromosome in low-folate medium. However, there were no significant differences in the total folate content or in the distribution of folate cofactors between fibroblasts from patients with the fragile X chromosome and those of controls both before and after a period of folate starvation. Fragile X and control fibroblasts lose folate at an equivalent rate. Insofar as folate content and distribution reflect a primary abnormality of folate metabolism, there appears to be no such abnormality in the fragile X syndrome. 相似文献
54.
55.
Some teichoic acids are known to be partially substituted by α-D-glucopyranosyl residues such as the teichoic acids of Streptococcus faecalis NCIB 8191. They will, therefore, bind specifically the phytohemagglutinin concanavalin A. Concanavalin A labelled with mercury or colloidal gold coated with concanavalin A has been used to mark isolated cell walls in order to localize the teichoic acids at the ultrastructural level. Besides these two direct marking techniques, the indirect concanavalin A-peroxidase technique (localization of peroxidase by the diaminobenzidine method followed by postosmication) has been applied to thin sections of premarked cells. All three methods gave almost identical results, namely, a dense and homogeneous distribution of the cell wall teichoic acids. In control experiments total inhibition was achieved in the presence of methyl-α-D-mannopyranoside. After trichloroacetic acid or alkali extraction of the teichoic acids from isolated walls no marking could be detected. 相似文献
56.
57.
H Klitgaard R Marc A Brunet H Vandewalle H Monod 《Journal of applied physiology》1989,67(4):1401-1408
To examine how different kinds of activity affect the composition and contractile properties of aging skeletal muscle, old male rats were strength and swim trained. The mass of weights lifted during the strength training increased by 85 +/- 9% (P less than 0.05), which was accompanied by an increase by 32 +/- 5% (P less than 0.05) of the estimated force developed. The wet muscle weight of the soleus and the plantaris decreased significantly with age. The phenomenon was counteracted but not neutralized by the strength training. Twitch and tetanic tension also decreased significantly with age in both the soleus and plantaris muscle. This was avoided by the strength training. This training also significantly decreased time to peak tension and half-relaxation time of both muscles. The swim training increased the heart-to-body weight ratio by 21 +/- 5% (P less than 0.05) and the endurance of the soleus muscle. Time to peak tension and triosephosphate dehydrogenase activity of the plantaris muscle were strongly correlated (P less than 0.001) with myosin adenosinetriphosphatase activity. The results show that the composition and contractile properties of old skeletal muscle are considerably affected by strength training repeated during a substantial period of old age, whereas swim training only affects the endurance of the skeletal muscle. 相似文献
58.
Marc Yudkoff David Pleasure Lynn Cregar Zhi-Ping Lin Ilana Nissim Janet Stern Itzhak Nissim 《Journal of neurochemistry》1990,55(1):137-145
The incorporation of [15N]glutamic acid into glutathione was studied in primary cultures of astrocytes. Turnover of the intracellular glutathione pool was rapid, attaining a steady state value of 30.0 atom% excess in 180 min. The intracellular glutathione concentration was high (20-40 nmol/mg protein) and the tripeptide was released rapidly into the incubation medium. Although labeling of glutathione (atom% excess) with [15N]glutamate occurred rapidly, little accumulation of 15N in glutathione was noted during the incubation compared with 15N in aspartate, glutamine, and alanine. Glutathione turnover was stimulated by incubating the astrocytes with diethylmaleate, an electrophile that caused a partial depletion of the glutathione pool(s). Diethylmaleate treatment also was associated with significant reductions of intraastrocytic glutamate, glycine, and cysteine, i.e., the constituents of glutathione. Glutathione synthesis could be stimulated by supplementing the steady-state incubation medium with 0.05 mM L-cysteine, such treatment again partially depleting intraastrocytic glutamate and causing significant reductions of 15N labeling of both alanine and glutamine, suggesting that glutamate had been diverted from the synthesis of these amino acids and toward the formation of glutathione. The current study underscores both the intensity of glutathione turnover in astrocytes and the relationship of this turnover to the metabolism of glutamate and other amino acids. 相似文献
59.
Marc Mangel 《Mathematical biosciences》1990,100(2):241-248
A patch selection game is formulated and analyzed. Organisms can forage in one of H patches. Each patch is characterized by the cost of foraging, the density and value of food, the predation risk, and the density of conspecifics. The presence of conspecifics affects the finding and sharing of food, and the predation risk. Optimal foraging theory can be viewed as a "1-person" game against nature in which the optimal patch choice of a specific organism is analyzed assuming that the number of conspecifics in other patches is fixed. In the general game theoretic approach, the behavior of conspecifics is included in the determination of the distinguished organism's strategy. An iterative algorithm is used to compute the solution of the "n-person" game or dynamic ESS, which differs from the optimal foraging theory solution. Experiments to test the proposed theory using rodents and seed trays are briefly discussed. 相似文献
60.
The organization of microtubules (MTs) in the cortex of cells at interphase is an important element in morphogenesis. Mechanisms
controlling the initiation of MTs and their spatial ordering, however, are largely unknown. Our recent study concerning the
generation of a radial array of MTs in stomatal guard cells inAllium showed that the MTs initiate in a cortical MT-organizing zone adjacent to the ventral wall separating the two young guard
cells (Marc, Mineyuki and Palevitz, 1989, Planta179, 516, 530). In an attempt to detect MT-ordering mechanisms separate from the sites of MT initiation, we now employ various
drugs to manipulate the geometry and integrity of the ventral wall and thereby also the associated MT-organizing zone. In
the presence of cytochalasin D the ventral wall is tilted away from its normal mid-longitudinal anticlinal alignment, while
treatments with the herbicide chloroisopropyl-N-phenylcarbamate (CIPC) induce the formation of a branched ventral wall. Nonetheless, in either case the MTs still
form a radial array, although this is asymmetric as it is centered in accordance with the misaligned or branched ventral wall.
Since the MTs maintain their original course undisturbed as they extend beyond the abnormal ventral wall, there is no evidence
for the presence of an inherent MT-ordering mechanism at locations remote from MT-initiation sites. Following treatments with
caffeine, which abolishes the formation of the ventral wall, the MTs revert to a transversely oriented cylindrical array as
in normal epidermal cells. Thus the presence of the ventral wall, and presumably also the associated MT-organizing zone, is
essential for the establishment of the radial array. The MT-organizing zone is therefore involved not only in the initiation
of MTs, but also in determining their spatial order throughout the cell cortex.
We thank Drs. Richard J. Cyr and Yoshi Mineyuki for providing valueable suggestions during the course of this work, and Ms.
Elizabeth Bruce printing some of the figures. This research was supported by Funds from the National Science Foundation grants
DCB-8703292 to B.A.P. and DCB-8803286 to B.A.P. and J.M. 相似文献