全文获取类型
收费全文 | 3091篇 |
免费 | 164篇 |
国内免费 | 2篇 |
出版年
2022年 | 14篇 |
2021年 | 32篇 |
2020年 | 21篇 |
2019年 | 28篇 |
2018年 | 45篇 |
2017年 | 28篇 |
2016年 | 64篇 |
2015年 | 83篇 |
2014年 | 111篇 |
2013年 | 195篇 |
2012年 | 178篇 |
2011年 | 176篇 |
2010年 | 118篇 |
2009年 | 88篇 |
2008年 | 207篇 |
2007年 | 154篇 |
2006年 | 143篇 |
2005年 | 183篇 |
2004年 | 180篇 |
2003年 | 174篇 |
2002年 | 170篇 |
2001年 | 58篇 |
2000年 | 81篇 |
1999年 | 59篇 |
1998年 | 38篇 |
1997年 | 37篇 |
1996年 | 29篇 |
1995年 | 33篇 |
1994年 | 28篇 |
1993年 | 17篇 |
1992年 | 49篇 |
1991年 | 42篇 |
1990年 | 48篇 |
1989年 | 34篇 |
1988年 | 25篇 |
1987年 | 41篇 |
1986年 | 34篇 |
1985年 | 26篇 |
1984年 | 26篇 |
1983年 | 18篇 |
1982年 | 15篇 |
1981年 | 16篇 |
1980年 | 14篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 12篇 |
1976年 | 10篇 |
1974年 | 9篇 |
1973年 | 8篇 |
1969年 | 7篇 |
排序方式: 共有3257条查询结果,搜索用时 15 毫秒
51.
New fluorescent rotor molecules having hydrophilic functional groups, which are derivatives of p-(N,N-dialkylamino)benzylidenemalononitrile, were synthesized. Their properties as fluorescent rotors were confirmed by an observation of solvent viscosity-dependent fluorescence. Incorporation of hydrophilic groups into the molecules increased the solubility of fluorescent rotors in aqueous media; the application of the compounds to biochemical systems became feasible as a consequence. To demonstrate this applicability, we attempted to monitor the G-F transformation of rabbit skeletal muscle actin with these newly synthesized compounds. All the compounds carrying a malononitrile moiety showed greater fluorescence in F-actin. Among them, 1-(2-hydroxyethyl)-6-[(2,2-dicyano)vinyl]-2,3,4-trihydroquinoli ne gave the best result by the criteria of the difference in fluorescence quantum yield for G- and F-actin, solubility, and stability of the compound. The method has the major advantage of not requiring covalent modification of actin. 相似文献
52.
53.
Hidekazu Sawada Takashi Suzuki Shun-ichi Akiyama Yoshio Nakao 《Applied microbiology and biotechnology》1990,32(5):556-559
Summary Gel-filtration analysis of a mixture of cyclodextrin (CyD) and lankacidin C showed that -CyD had strong, -CyD weak and -CyD no affinity for lankacidin C. Lankacidin C production activity, which was assayed by measuring the incorporation of l-[methyl-14C-]methionine into the lankacidin molecule, was the greatest with cells grown in the presence of -CyD, less with -CyD and the least with -CyD. Lankamycin and T-2636M, which are by-products in lankacidin C fermentation, were not included by -CyD and their production was not stimulated by -CyD. It was apparent that the stimulatory effect of CyD was closely related to the formation of an inclusion complex between CyD and the antibiotic. Lankacidin C biosynthesis was repressed by preincubating cells with lankacidin C, while the repressive effect of lankacidin C was abrogated by the inclusion by -CyD. Thus, abrogation of feed-back repression seems to be a main mechanism of the effect of CyD. However, -CyD, which had no affinity for lankacidin C, stimulated the production to the least extent and exhibited a complementary effect on the stimulation by -CyD or -CyD. -CyD also caused a change in cell morphology and cell-surface hydrophobicity. It was assumed that the modification of the cell surface is a secondary mechanism of the effect of CyD.The second report of the stimulatory effect of cyclodextrins on lankacidin fermentationOffprint requests to: H. Sawada 相似文献
54.
Spatial distribution pattern of the brown planthopper (BPH) was analyzed at 9 experimental fields in the northern part of West Java during two consecutive rice cropping seasons, i.e., wet and dry seasons. The population of each developmental stage and wing form of BPH at each location showed consistent departure from the random (Poisson) distribution, the variances of the densities in most cases exceeding their means. Namely, the distribution pattern of BPH per hill of rice plant was found to have a general tendency to be aggregated or contagious and to fit fairly well to the negative binomial model. The tendency for aggregation was further confirmed by both the β-values of -m regression being larger than unity and the CA-values being larger than zero for each developmental stage. Although significant variations in the distribution pattern as measured by β- or CA-value were observed between different developmental stages, between wing forms and among locations, the degree of aggregation for a given developmental stage at each experimental field remained fairly stable throughout the crop period, despite wide temporal changes in population density. Possible factors to explain these characteristics of the spatial distribution pattern of the BPH in West Java were discussed with reference to the process generating it. 相似文献
55.
Minamisawa Kiwamu; Ogawa Ken-Ichiro; Fukuhara Hideyuki; Koga Jinichiro 《Plant & cell physiology》1996,37(4):449-453
Indole-3-acetaldehyde (IAAId) was detected in the culture supernatantof Bradyrhizobium elkanii. Deuteriumlabelled L-tryptophan (Trp)was incorporated into IAAId and indole-3-acetic acid (IAA),suggesting that B. elkanii produces IAA via IAAId from Trp.In B. elkanii cell suspension, indole-3-pyruvic acid (IPyA)was converted to IAAId, and exogenously added IAAId was rapidlyconverted to IAA. Furthermore, the activity of indolepyruvatedecarboxylase (IPDC), which catalyzes the decarboxylation ofIPyA to produce IAAId and is a key enzyme for IPyA pathway,was detected in B. elkanii cell-free extract. The IPDC activitydepended on Mg2+ and thiamine pyrophosphate, cofactors of decarboxylation.This mounting evidence strongly suggests that IAA synthesisoccurs via IPyA pathway (Trp IPyA p IAAId IAA) in B. elkanii. (Received December 11, 1995; Accepted March 4, 1996) 相似文献
56.
In rodents an intravenous administration of viableCryptococcus (C.) neoformans cells frequently resulted in attachment of intravascular cryptococcal granulomas to inner walls of the large to medium-sized
veins of various organs, including the lungs, liver and spleen. In order to elucidate the pathogenesis of granulomatous changes,
the cells composing the intravascular granulomas were observed by electron microscopic peroxidase (PO) cytochemistry. The
granuloma composing cells could be divided into the following four types according to the pattern of endogenous peroxidase
activity: exudate macrophage (Mφ, type I), PO-negative Mφ (type II), resident Mφ (type III) and other inflammatory cells (type
IV). In the intravenous granulomas of the lung, the percentages of composed cells were 39.0% for type I, 57.9% for type II,
0% for type III and 3.1% for type IV. By contrast, in the interstitial granulomas in the lung, type III Mφs, possibly derived
from alveolar Mφs, played a significant role in granuloma formation. This may indicate that the intravascular granuloma is
almost composed of macrophages derived from monocytes rather than alveolar macrophages. The expression of ICAM-1 on endothelia
of the pulmonary veins was examined by immunoelectron microscopy. An immunogold labeling index was significantly augmented
on the surface of endothelia in response to intravenous challenge ofC. neoformans. The intravascular granuloma demonstrates that the monocytes develop into the granuloma-composing macrophages and suppress
the cryptococcal activities even hi the peripheral blood resulting in an assistance of endothelial functions. 相似文献
57.
The effects of dwarf bamboo,Sasa, cover on the initial morrality of hardwood seedlings were investigated by transplanting 1-year-old beech (Fagus crenata) and current-year oak (Quercus mongolica var.grosseserrata) seedling to three different stands; old-growth beech and secondary oak forests withSasa undergrowth, and aSasa grassland in a grassland-forest series near the top of Mt Jippo, southwestern Japan. The most frequent cause of seedling
morrality was gnawing of the stems by rodents. In the beech forest, the gnawing was more likely to occur underSasa cover, suggesting that it provides a good habitat for rodents on the beech forest floor. TheSasa under growth may thus play an imporrant role in regeneration of beech forest. In the oak floor, mortality of both species
was low and only a little gnawing occurred during a year. However, no natural oak seedling were found in the forest even after
a mast year. This may be because most of the acorns disappeated before establishment. The early-stage demography of hardwood
seedling as oak may thus play an imporrant role in regeneration of oak forest. In theSasa grassland where the seed supply is small, almost all of the seedlings died fromo gnawing regardless of the presence ofSasa cover. These factors prevent the recruitment of a sizable seedling bank. Rodents may thus play an imporrant role in maintenance
of theSasa grassland. 相似文献
58.
It has been proposed that peg formation in the vascular transition region (TR zone) between the hypocotyl and the root in
Cucurbitaceae seedlings is a gravimorphogenetic phenomenon. Initiation of the peg became visible 36 h after imbibition when
cucumber (Cucumis sativus L. cv. Burpee Hybrid II) seeds were germinated in a horizontal position at 24°C in the dark. Simultaneously, sedimented amyloplasts
(putative statoliths) were apparent in the sheath cells surrounding the vascular strands, and in the cortical cells immediately
adjacent to them, in the TR zone. In contrast, the other cortical cells, some of which were destined to develop into the peg,
contained amyloplasts which were not sedimented. These results suggest that the graviperception mechanism for peg formation
may be like that of statoliths in shoot gravitropism. By 48 h following imbibition, the cells of the TR zone still had sedimented
amyloplasts but had lost their sensitivity to gravity, possibly because of their maturation. 相似文献
59.
Shoko Fujiwara Mitsuhiro Sawada Junichiro Someya Nobuhiro Minaka Masanobu Kawachi Isao Inouye 《Journal of phycology》1994,30(5):863-871
The nucleotide sequences of rbcL genes encoding the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) were determined from six species of Prymnesiophyta to clarify their phylogenetic relationships. Molecular phylogenetic trees were constructed using PAUP (Phylogenetic Analysis Using Parsimony). These analyses suggest that the Prymnesiophyta, except for the Pavlovales, area relatively stable monophyletic group. Pleurochrysis carterae, included in the Isochrysidales, is a sister species of a monophyletic group consisting of other members of the Isochrysidales, Gephyrocapsa oceanica and Emiliania huxleyi, members of the Coccosphaerales, Calyptrosphaera sphaeroidea and Umbilicosphaera sibogae var. foliosa, and a member of the Prymnesiales, Chrysochromulina hirta. The nucleotide sequence of rbcL from G. oceanica was identical to that from E. huxleyi within the region examined. Our trees show that G. oceanica and E. huxleyi are more closely related to C. hirta than to U. sibogae, C. sphaeroidea, and P. carterae. These results suggest that orders in the Prymnesiophyceae, including the above-mentioned genera, should be redefined. 相似文献
60.
Hideyuki Takahashi 《Plant and Soil》1994,165(2):301-308
We have studied hydrotropism and its interaction with gravitropism in agravitropic roots of a pea mutant and normal roots of peas (Pisum sativum L.) and maize (Zea mays L.). The interaction between hydrotropism and gravitropism in normal roots of peas or maize were also examined by nullifying the gravitropic response on a clinostat and by changing the stimulus-angle for gravistimulation. Depending on the intensity of both hydrostimulation and gravistimulation, hydrotropism and gravitropism of seedling roots strongly interact with one another. When the gravitropic response was reduced, either genetically or physiologically, the hydrotropic response of roots became more unequivocal. Also, roots more sensitive to gravity appear to require a greater moisture gradient for the induction of hydrotropism. Positive hydrotropism of roots occurred due to a differential growth in the elongation zone; the elongation was much more inhibited on the moistened side than on the dry side of the roots. It was suggested that the site of sensory perception for hydrotropism resides in the root cap, as does the sensory site for gravitropism. Furthermore, an auxin inhibitor, 2,3,5-triiodobenzoic acid (TIBA), and a calcium chelator, ethyleneglycol-bis-(-aminoethylether)-N,N,N,N- tetraacetic acid (EGTA), inhibited both hydrotropism and gravitropism in roots. These results suggest that the two tropisms share a common mechanism in the signal transduction step. 相似文献