全文获取类型
收费全文 | 3337篇 |
免费 | 302篇 |
国内免费 | 87篇 |
出版年
2024年 | 5篇 |
2023年 | 92篇 |
2022年 | 100篇 |
2021年 | 205篇 |
2020年 | 196篇 |
2019年 | 206篇 |
2018年 | 130篇 |
2017年 | 104篇 |
2016年 | 104篇 |
2015年 | 153篇 |
2014年 | 195篇 |
2013年 | 207篇 |
2012年 | 161篇 |
2011年 | 193篇 |
2010年 | 147篇 |
2009年 | 172篇 |
2008年 | 178篇 |
2007年 | 165篇 |
2006年 | 125篇 |
2005年 | 116篇 |
2004年 | 110篇 |
2003年 | 87篇 |
2002年 | 81篇 |
2001年 | 78篇 |
2000年 | 52篇 |
1999年 | 53篇 |
1998年 | 37篇 |
1997年 | 36篇 |
1996年 | 30篇 |
1995年 | 28篇 |
1994年 | 23篇 |
1993年 | 22篇 |
1992年 | 20篇 |
1991年 | 10篇 |
1990年 | 16篇 |
1989年 | 10篇 |
1988年 | 14篇 |
1987年 | 3篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 4篇 |
1972年 | 1篇 |
排序方式: 共有3726条查询结果,搜索用时 15 毫秒
11.
12.
LAURENCE M. COOK 《Biological journal of the Linnean Society. Linnean Society of London》2007,90(1):49-53
A test has been made of the association of heterozygosity with shell breadth in the polymorphic snail Cepaea nemoralis. The material was collected by C. B. Goodhart from a series of paired sites at which individuals reached different adult breadths. Dominant phenotypes, in which a large fraction was heterozygous, had a greater breadth and lower variance than recessive phenotypes regardless of whether the measurement was of shell ground colour, banding or the double recessive vs. the rest. Most of the difference was contributed by samples from the habitat where animals reached the largest size. The result is consistent with existence of heterotic sections of chromosome that include the colour and banding loci, and may help to explain the persistence of the polymorphism. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 49–53. 相似文献
13.
14.
The relationship between prominent visual imagery and emotion within dreams was investigated in relation to E. Hartmann's (1996) contextualizing image (CI) theory and M. Seligman and A. Yellen's (1987) dual imagery theory. Fifty-nine students recorded dreams over a 2-week period and submitted 115 dreams for analysis. Participants recorded ratings of emotion type and emotion intensity in each scene. Prominent visual images were identified and scored for intensity and detail by independent judges. As hypothesized from Hartmann's theory, there was a significant positive relationship between CI intensity and emotion intensity in the CI scene, emotion intensity generally peaked in the CI scene, and dreams containing a CI had higher overall ratings of emotion intensity than non-CI dreams. The result for the correlation of detail of prominent imagery with emotion was inconclusive, with a low positive correlation across CI scenes. This raises the possibility that the CI is not a unitary construct. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
15.
D. EISIKOWITCH Z. LAZAR 《Botanical journal of the Linnean Society. Linnean Society of London》1987,95(2):101-111
Flower change in Oenothera drummondii Hooker as a response to pollinators' visits. The colour and shape of flowers of Oenothera drummondii change owing to senescence, pollination and/or nectar withdrawal. This phenomenon is interpreted as a signal emitted by the plant to 'inform' the potential pollinator of its new status as a rewardless flower. This method of signalling might be important for the pollinators in order to save energy in seeking the correct flowers and for the plant to ensure visits to those flowers that have not yet been visited. 相似文献
16.
Tomato (Lycopersicon esculentum Mill. cv. Moneymaker) plants have been wounded to induce the accumulation of proteinase-inhibitor proteins (PI proteins) at the local site of injury and systemically in unwounded tissues. To determine the range of genes affected in the wound-response, polysomal mRNA has been isolated from the damaged leaves and from systemically responding leaves over a time-course of 2, 4, 10 and 24 h after wounding. Changes in the pattern of 35S-translation products indicate that the events that occur at the local wound-site are different from those that occur systemically, both with respect to the number of genes that are regulated and the timing of their regulation. In order to compare the effects of wounding and an endogenous systemic signal generated at the wound-site with those of elicitor (proteinase-inhibitor-inducing factor, PIIF) treatment of excised plants, polysomal mRNA has also been isolated from leaves of plants over a time-course of 2, 4, 10 and 24 h after PIIF-treatment. Changes in the pattern of 35S-translation products indicates that the events induced by PIIF resemble those induced by mechanical injury, rather than those induced by the endogenous systemic signal.Abbreviations IFF
isoelectric focussing
- PI proteins
proteinase inhibitor proteins
- PIIF
proteinase-inhibitor-inducing factor
- ssRubisco
small subunit of ribulose-1,5-bisphosphate carboxylase 相似文献
17.
Insulin signal transmission through the plasma membrane was studied in terms of relationship between basal autophosphorylation of the β-subunit and the ability by bind insulin by the -subunit of the insulin receptor. In a cell free system, receptors phosphorylated on tyrosine residues in the absence of insulin were separated from non-phosphorylated receptors using antiphosphotyrosine antibodies. Insulin binding assays were then performed on basally autophosphorylated and on non-phosphorylated receptors. We found that the tyrosine phosphorylated receptors, which corresponded to 25% of the total number of receptors, were accountable for 60–80% of insulin binding. Scatchard representation of binding data has shown that the plot corresponding to tyrosine phosphorylated receptors was localized above, and was steeper than the plot corresponding to non-phosphorylated receptors. These data make it likely that the conformation of -subunit which favours ligand binding is connected to the conformation of β-subunit which favours phosphate reception on tyrosine residues. Reciprocally, the high-affinity conformation of insulin receptor seems to become stabilized by basal autophosphorylation. 相似文献
18.
Prof. Dr. Dick R. Nässel Mats H. Holmqvist Roger C. Hardie Rolf Håkanson Frank Sundler 《Cell and tissue research》1988,253(3):639-646
Summary Antibodies to histamine were used for immunocytochemical studies of the visual system in the flies Calliphora erythrocephala and Musca domestica. Specific immunolabeling of photoreceptors was found both in the compound eyes and ocelli of both species. In the compound eyes histamine-like immunoreactivity (HA-IR) was found in all the short visual fibers (photoreceptors R1–6) and one type of long visual fiber (photoreceptor R8). In addition, the ocellar photoreceptors also show HA-IR. In view of earlier biochemical and pharmacological/physiological findings by Elias and Evans (1983) and Hardie (1987) it thus seems likely that histamine is a neurotransmitter in insect photoreceptors. Interestingly, the second type of long visual fiber (photoreceptor R7) has recently been found to be GABA-immunoreactive (Datum et al. 1986). The two types of long visual fibers may hence use different transmitters which act on different receptors of the postsynaptic neurons in the second visual neuropil, the medulla. In addition to the photoreceptors in the retina and ocelli, we found processes of HA-IR neurons in one of the optic lobe neuropils, the lobula. This finding indicates that histamine may also be a transmitter in certain interneurons in the visual system.Abbreviations
HA
histamine
-
GABA
-amino butyric acid
-
GAD
glutamic acid decarboxylase
-
5-HT
5-hydroxytryptamine (serotonin)
-
HA-IR
histamine-like immunoreactivity
-
R1-R6
class of short-axoned photoreceptors
-
R7 and R8
long-axoned photoreceptors
-
LMC
large monopolar neuron of lamina
-
HSA
human serum albumin
-
PBS
phosphate-buffered saline
-
DEPC
diethylpyrocarbonate 相似文献
19.
Abstract. The techniques of molecular biology are being employed to investigate at the gene level the systemically mediated, wound-induced accumulation of two defensive proteinase inhibitor proteins in plant leaves. These techniques have added a new dimension to biochemical and physiological studies already underway to understand the mechanism of induction by wounding. The acquisition of cDNAs from the RNAs coding for the two inhibitors facilitated studies of mRNA synthesis in leaves in response to wounding, and provided probes to obtain wound-inducible proteinase inhibitor genes from tomato ( Lycopersicon esculentum ) and potato (Solarium tuberosum) genomes. Successful transformations of tobacco plants with fused genes, containing the 5' and 3' regions of the inhibitor genes with the open reading frame of the chloramphenicol acelyltransferase ( cat ) gene, have provided a wound-inducible chloramphenicol acetyltransferase (CATase) activity with which to seek cis- and transacting elements that regulate wound-inducibility to help to understand the interaction of cytoplasmic and nuclear components of the intracellular communication systems that activate the proteinase inhibitor genes in response to wounding by insect pests. 相似文献
20.
Martin Cambray-Deakin Brian Pearce Christine Morrow Sean Murphy 《Journal of neurochemistry》1988,51(6):1846-1851
Astrocyte-enriched and meningeal cell cultures of the rat cerebral cortex were prepared, and their glycogen content was measured after 10-90 min under control (2.5 mM) concentrations of potassium after prefeeding with 20 mM glucose. No net change in glycogen level was noted in either culture over this period. Cell cultures were then exposed to increased concentrations of potassium (5, 10, and 15 mM), and their glycogen content was measured after 10-90 min. Both types of cell culture showed complex and variable changes in glycogen content. In general, increased potassium concentrations caused astrocyte glycogen stores to be reduced at physiological increases of potassium levels (from 2.5 to 5 mM and above), although a period of resynthesis was evident at all potassium concentrations. Meningeal cell glycogen levels were highly variable and only affected by high (10 and 15 mM) levels of potassium. These results are discussed with respect to the theory that changes in the external potassium concentration caused by neuronal activity might act as a signal controlling astrocyte glycogen stores. 相似文献