全文获取类型
收费全文 | 2830篇 |
免费 | 230篇 |
国内免费 | 4篇 |
出版年
2023年 | 20篇 |
2022年 | 43篇 |
2021年 | 103篇 |
2020年 | 49篇 |
2019年 | 65篇 |
2018年 | 77篇 |
2017年 | 54篇 |
2016年 | 90篇 |
2015年 | 171篇 |
2014年 | 194篇 |
2013年 | 218篇 |
2012年 | 218篇 |
2011年 | 231篇 |
2010年 | 151篇 |
2009年 | 116篇 |
2008年 | 165篇 |
2007年 | 163篇 |
2006年 | 142篇 |
2005年 | 136篇 |
2004年 | 134篇 |
2003年 | 114篇 |
2002年 | 81篇 |
2001年 | 20篇 |
2000年 | 15篇 |
1999年 | 18篇 |
1998年 | 26篇 |
1997年 | 21篇 |
1996年 | 10篇 |
1995年 | 18篇 |
1994年 | 21篇 |
1993年 | 22篇 |
1992年 | 13篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 9篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有3064条查询结果,搜索用时 36 毫秒
31.
Alexander A. Bachmanov Danielle R. Reed Yuro Ninomiya Masashi Inoue Michael G. Tordoff R. Arlen Price Gary K. Beauchamp 《Mammalian genome》1997,8(8):545-548
Individual variability in sucrose consumption is prominent in humans and other species. To investigate the genetic contribution
to this complex behavior, we conducted behavioral, electrophysiological, and genetic studies, using male progeny of two inbred
mouse strains (C57BL/6ByJ [B6] and 129/J [129]) and their F2 hybrids. Two loci on Chromosome (Chr) 4 were responsible for over 50% of the genetic variability in sucrose intake. These
loci apparently modulated intake by altering peripheral neural responses to sucrose. One locus affected the response threshold,
whereas the other affected the response magnitude. These findings suggest that the majority of difference in sucrose intake
between male B6 and 129 mice is due to polymorphisms of two genes that influence receptor or peripheral nervous system activity.
Received: 27 January 1997 / Accepted: 17 March 1997 相似文献
32.
Propylthiouracil Tasting: Determination of Underlying Threshold Distributions using Maximum Likelihood 总被引:2,自引:1,他引:1
Reed Danielle R.; Bartoshuk Linda M.; Duffy Valarie; Marino Susan; Price R. Arlen 《Chemical senses》1995,20(5):529-533
The ability to taste low concentrations of propylthiouracil(PROP) and related bitter compounds is heritable. The currentanalysis determines whether the distribution of PROP taste thresholdsis consistent with an additive or a dominant mode of Mendeliantransmission. To that end, the lowest concentration of PROPdetectable was determined for 1015 subjects and models of bi-or tri-modal distributions of PROP taste thresholds were tested.The model with the greatest likelihood had three distributionsand followed an additive model of PROP taste sensitivity ifthe variances associated with the distributions were assumedto be equal. However, if the taste thresholds were transformedto remove skewness, or if the variances were unequal, then three-or two-distribution models were equally likely. Resolution ofthe mode of inheritance for bitter taste perception awaits additionalfamily studies and the characterization of the molecular basisof taste perception for these bitter compounds. Chem. Senses20: 529533, 1995. 相似文献
33.
Summary Periplasmic-leaky (lky) Hfr mutant strains of Escherichia coli K12, grown in low-phosphate Tris medium, excreted alkaline phosphatase (AP) into the extracellular fluid. The lky207 mutation, which proved to induce the highest AP excretion rate, was transferred to an F- host, carrying a phoS, T mutation allowing constitutive AP biosynthesis. Use of high-phosphate LB-rich medium for growing this F-
lky strain improved cell biomass, extracellular AP activity and excretion specificity in favour of the enzyme. Physiological studies helped us to develop a new culture medium (LB 8.3) giving higher enzyme and excretion yields. LB 8.3 medium also increased cell viability of lky mutants stored at 4° C.Using optimized culture conditions, the highest extracellular enzyme activity produced by lky mutant 706 was reached in the late stationary growth phase and was equal to 1,400 U/ml of culture medium (i.e., 6 times the intracellular AP content of wild-type strain, Ga15, developed in derepressed conditions); AP released into the extracellular fluid corresponded to 34% of total excreted proteins and was equivalent to a purified enzyme preparation. 相似文献
34.
In direct measurements of phage λ DNA synthesis, we have detected an inhibition caused by the cII and cIII gene products. This inhibition was more clearly observed when P amber phages were grown in a permissive host, presumably because of the limitation in DNA synthesis due to uncomplete suppression. The inhibition takes place in cells infected at high multiplicity, but not in cells infected at low multiplicity. To explain these findings, we propose a model in which the bacterial population is heterogeneous with respect to its ability to support phage DNA synthesis. An initial limitation caused by host factors would be amplified by the action of the cII and cIII products, at high multiplicity only, and the resulting inhibition would be essential in the « choicetowards lysogeny. 相似文献
35.
Granulosa cells of antral follicles both proliferate and undergo differentiation. The aim of the present work was to study the mechanisms controlling the balance between proliferation and differentiation in granulosa cells during the development of antral follicles in the ewe. For this purpose, the responses of both activities to insulin-like growth factor-I (IGF-I) and to FSH in vitro were studied comparatively in granulosa cells from small antral follicles (1-3 mm in diameter) and large antral follicles (5-7 mm in diameter). In granulosa cells from large follicles, IGF-I enhanced both basal and FSH-induced progesterone secretion after a 24-h delay period; this effect was lower and further delayed in cells from small follicles. Reciprocally, FSH increased IGF-I-stimulated progesterone secretion in cells from large follicles. IGF-I increased the thymidine labeling index of granulosa cells from small follicles within 24 h and enhanced cell multiplication. In cells from large follicles, this effect was lower and delayed, but IGF-I also enhanced cell survival. Culture at high density of plating inhibited the proliferative response of both types of cells to IGF-I. FSH was without effect on granulosa cell multiplication. These results suggest that the cytodifferentiative and the growth-promoting effects of IGF-I are clearly distinct. We propose that they would be exerted on two distinct granulosa cell subpopulations, nonproliferating and proliferating cells, respectively. Differences in the responsiveness of cells from small and large follicles could be related to differences in the proportion of these two cellular subtypes. 相似文献
36.
Characteristics of thermoluminescence glow curves were compared in three types of Euglena cells: (i) strictly autotrophic, Cramer and Myers cells; (ii) photoheterotrophic cells sampled from an exponentially growing culture containing lactate as substrate repressing the photosynthetic activity; (iii) semiautotrophic cells, sampled when the lactate being totally exhausted, the photosynthesis was enhanced.In autotrophic and semiautotrophic cells, composite curves were observed after series of two or more actinic flashes fired at –10°C, which can be deconvoluted into a large band peaking in the range 12–22°C and a smaller one near 40°C, This second band presents the characteristics of a typical B band (due to S2/3QB
- recombination), whereas the first one resembled the band, shifted by -15–20°C, which is observed in herbicide resistant plants. The amplitude of this major band, which was in all cases very low after one flash, exhibited oscillations of period four but rapidly damping, with maxima after two and six flashes. In contrast, photoheterotrophic Euglena displayed single, non-oscillating curves with maxima in the range 5–10°C.In autotrophic and semiautotrophic cells, oxidizing pretreatments by either a preillumination with one or more (up to twenty-five) flashes, or a far-red preillumination in the presence of methylviologen, followed by a short dark period, induced thermoluminescence bands almost single and shifted by +3–5°C, or +12°C, respectively. In autotrophic cells, far-red light plus methyl viologen treatment induced a band peaking at 31°C, as in isolated thylakoids from Euglena or higher plants, while it had barely any effect in photoheterotrophic cells.Due to metabolic activities in dark-adapted cells, a reduction of redox groups at the donor and acceptor sides of PS II dark-adapted cells is supposed to occur. Two different explanations can be proposed to explain such a shift in the position of the main band in dark-adapted autotrophic control. The first explanation would be that in these reducing conditions a decreasing value of the equilibrium constant for the reaction: SnQA
-QBSnQAQB
-, would determine the shift of the main TL band towards low temperatures, as observed in herbicide resistant material. The second explanation would be that the main band would correspond to peak III already observed in vivo and assigned to S2/3QB
2- recombinations.Abbreviations CM
Cramer and Myers
- D1
a 32 kDa protein component of the PS II reaction center, psbA.gene product
- D2
a 34 kDa protein component of the PS II reaction center, psbD gene product
- FR
lar-red illumination
- Lexpo and Lstat
cells from lactate culture samples at exponential and stationary phase of growth
- MV
methylviologen
- pBQ
parabenzoquinone
- PQ
plastoquinone
- PS II
photosystem II
- QA
primary quinone electron acceptor
- QB
secondary quinone electron acceptor
- TL
thermoluminescence 相似文献
37.
Phyto- and bacterioplankton biomass and activity were simultaneously measured during the course of one year in the shallow Créteil Lake (France).Phytoplankton was dominated, during the whole year, by small-sized organisms (10 to 25 µm). Bacteria were in a majority small coccoids (<0.3 µm). Phyto -and bacterioplankton abundances averaged respectively 3.3 × 106 cells l–1 and 6 × 109 cells l–1.The phasing of the activity and biomass periods suggest a close coupling between phyto- and bacterioplankton. There were two distinct periods of high activity and biomass. Maximal values were observed in summer but an early increase occurred also in winter. Low or undetectable phytoplankton excretion rates, when heterotrophic activity was maximum, indicated a bacterial uptake of up to 100% of the released algal products during the incubation period. Heterotrophic uptake measurements with both glucose and amino acids revealed a seasonal change of the substrates in the lake, glucose uptake being associated more with the maximum activity of the algae, while the amino acids uptake was relatively higher during their decline.The maximal photosynthetic rate averaged 21.5 mgC m–3 h–1 and mean Vmax values were 0.056 and 0.050 mgC m–3 h–1 respectively for glucose and amino acids uptake. 相似文献
38.
39.
Neurochemical Studies of the Mesolimbic Dopaminergic Pathway: Somatodendritic Mechanisms and GABAergic Neurones in the Rat Ventral Tegmentum 总被引:6,自引:4,他引:2
Abstract: The rat ventral tegmentum (containing dendrites and somata of mesolimbic neurones) contained 1.3 μg/g of dopamine, which was reduced to 40% of the control level by reserpine. Slices of ventral tegmentum were able to accumulate and release (elevated potassium or protoveratrine A) exogenous [3 H]dopamine. In parallel studies the uptake mechanism in ventral tegmentum was shown to be virtually identical to the nerve terminal uptake of [3 H]dopamine by slices of nucleus accumbens. The release of [3 H]dopamine was indistinguishable from that observed in substantia nigra, where there is substantial evidence for dendritic mechanisms. Basal adenylate cyclase activity was present, but dopamine-stimulated activity was not detected. A high GABA concentration (7.7 μmol/g) was present in ventral tegmentum, in conjunction with an uptake and a release mechanism for [3 H]GABA. GABA and muscimol elicited a small, reproducible efflux of [3 H]dopamine, but an interaction between dopamine and [3 H]GABA efflux was not observed. The results are in accord with transmitter roles for dopamine and GABA in the somatoden-dritic area of mesolimbic dopaminergic neurons. 相似文献
40.
Patrice C. Dubreuil Daniel Z. Birnbaum Danielle H. Caillol Francois A. Lemonnier 《Immunogenetics》1982,16(5):407-424
The inhibitory capacity of 17 monoclonal antibodies (m.Ab.) specific for the products of the I-A
k
subregion was evaluated in proliferative responses of B10.BR T-lymphocytes to GAT, Keyhole limpet hemocyanin, and ovalbumin. Considered in isolation, each m.Ab. mediated inhibitory effects of comparable magnitude on these three different proliferative responses. On the other hand, clear differences were observed when the magnitude of the inhibitory effects was compared from one m.Ab. to another. The m.Ab. were consequently classified as strong or moderate-to-weak inhibitors of T-cell proliferative responses. Evidence was simultaneously gained indicating the following: (a) the determinants recognized by different m.Ab. were expressed on the same molecules; (b) the differences in affinity of the m.Ab. for I-Ak positive cells did not explain their differences in inhibitory capacities; (c) conversely, the inhibitory capacity of each m.Ab. followed its ability to inhibit the cell surface fixation of Ia.17-specific 10-2.16 m.Ab.; (d) the strong inhibitory capacity of some m.Ab. was not related to a special ability to modulate cell surface Ia molecules. These results suggest that antigen recognition by T lymphocytes is preferentially restricted by a functional site of the I-Ak molecules related to the Ia.17 and Ia.1 specificities.Abbreviations EDTA
Ethylenediamine-tetraacetic acid disodium salt
- EHAA
Eagle's Hanks' amino acids medium
- FCS
fetal calf serum
- in polypeptide
G is glutamate, A, alanine, T, tyrosine
- HEPES
N-2-hydroxy-piperazine-N-2-ethane sulfonic acid
- kd
dissociation rate constant
- KLH
Keyhole limpet hemocyanin
- LPS
lipopolysaccharide
- m.Ab.
monoclonal antibodies
- NP-40
nonidet P-40
- PBS
phosphate buffered saline
- PBS-BSA
PBS supplemented with 1% bovine serum albumin
- PBS-BSA-NP-40
PBS-BSA supplemented with 0.5% NP-40
- RT
room temperature
- SEM
standard error of the mean
- s.c.
spleen cells 相似文献