全文获取类型
收费全文 | 2477篇 |
免费 | 345篇 |
国内免费 | 45篇 |
出版年
2021年 | 42篇 |
2017年 | 29篇 |
2016年 | 40篇 |
2015年 | 62篇 |
2014年 | 82篇 |
2013年 | 88篇 |
2012年 | 95篇 |
2011年 | 106篇 |
2010年 | 71篇 |
2009年 | 64篇 |
2008年 | 85篇 |
2007年 | 90篇 |
2006年 | 91篇 |
2005年 | 75篇 |
2004年 | 78篇 |
2003年 | 73篇 |
2002年 | 80篇 |
2001年 | 68篇 |
2000年 | 94篇 |
1999年 | 50篇 |
1998年 | 38篇 |
1997年 | 30篇 |
1996年 | 29篇 |
1995年 | 32篇 |
1993年 | 27篇 |
1992年 | 50篇 |
1991年 | 56篇 |
1990年 | 47篇 |
1989年 | 34篇 |
1988年 | 38篇 |
1987年 | 43篇 |
1986年 | 42篇 |
1985年 | 55篇 |
1984年 | 38篇 |
1983年 | 34篇 |
1982年 | 28篇 |
1981年 | 30篇 |
1980年 | 38篇 |
1979年 | 35篇 |
1978年 | 29篇 |
1977年 | 36篇 |
1976年 | 31篇 |
1975年 | 34篇 |
1974年 | 35篇 |
1973年 | 38篇 |
1972年 | 36篇 |
1971年 | 29篇 |
1970年 | 28篇 |
1969年 | 24篇 |
1968年 | 28篇 |
排序方式: 共有2867条查询结果,搜索用时 15 毫秒
101.
An aqueous extract of bovine pineal tissue contained a principle which caused a potent inhibition of ACTH mediated corticosterone release by isolated adrenal cells, whereas a similar extract of cortical tissue did not have any effect on this process. Two pineal indoles were tested. Melatonin (10?8 M) did not have any significant effect, whereas 5-methoxytryptophol (10?8 M) caused a variable but significant additive effect on ACTH mediated corticosterone release. We are uncertain at the present time if this principle is similar to the reported pinealantigonadotropin. 相似文献
102.
C-Glycosylflavones have been identified in Ephedra antisyphilitica, Gnetum gnemon and Welwitschia mirabilis. The C-glycosidic moieties of apigenin and luteolin derivatives have been identified as glucose and/or xylose for these species. 相似文献
103.
John R. Porter Michael F. Allen Leslie C. Lane Michael G. Boosalis 《Plant and Soil》1982,68(2):283-287
Summary A chlorotic condition of soybeans in the river valleys of eastern Nebraska was studied. The pattern of chlorosis, presence
of petiolar necrosis, reductions in rhizobial and mycorrhizal infection, and plant and soil chemical analyses suggest that
the condition is more complex than normal iron deficiency chlorosis or other mineral deficiencies or toxicities. Nodulation
is almost totally inhibited in affected plants. Mycorrhizal fungi, while able to infect early in the season, do not persist
on affected plants. Breakdown of endodermis was observed in the roots of affected plants. The factors contributing to this
condition have not yet been determined.
Published with the approval of the director as Paper No. 5672, Journal Series, Nebraska Agricultural Experiment Station. 相似文献
104.
We report fluorescence lifetimes for in vivo chlorophyll a using a time-correlated single-photon counting technique with tunable dye laser excitation. The fluorescence decay of dark-adapted chlorella is almost exponential with a lifetime of 490 ps, which is independent of excitation from 570 nm to 640 nm.Chloroplasts show a two-component decay of 410 ps and approximately 1.4 ns, the proportion of long component depending upon the fluorescence state of the chloroplasts. The fluorescence lifetime of Photosystem I was determined to be 110 ps from measurements on fragments enriched in Photosystem I prepared from chloroplasts with digitonin. 相似文献
105.
The pattern of protein synthesis was compared in several organs of maize (Zea mays L.) under aerobic and anaerobic conditions. Protein synthesis was measured by [35S]methionine incorporation and analysis by two-dimensional native-SDS (sodium lauryl sulfate) polyacrylamide gel electrophoresis and fluorography. The aerobic protein-synthesis profiles were very different for root, endosperm, scutellum and anther wall. However, except for some characteristic qualitative and quantitative differences, the patterns of protein synthesis during anaerobiosis were remarkably similar for these diverse organs and also for mesocotyl and coleoptile. The proteins synthesized were the anaerobic polypeptides (ANPs) which have been previously described in anaerobic roots of seedlings. Leaves exhibited no detectable protein synthesis under anaerobic conditions, and died after a short anaerobic treatment. Evidence is presented that the ANPs are not a generalized response to stress. This indicates that the ANPs are synthesized as a specific response to anaerobic conditions such as flooding.Abbreviations ADH
alcohol dehydrogenase
- ANP
anaerobic polypeptide
- SDS
sodium lauryl sulfate 相似文献
106.
Mutants of vesicular stomatitis virus blocked at different stages in maturation of the viral glycoprotein 总被引:49,自引:0,他引:49
Maturation of the vesicular stomatitis virus (VSV) glycoprotein (G) to the cell surface is blocked at the nonpermissive temperature in cells infected with temperature-sensitive mutants in the structural gene encoding for G. We show here that these mutants fall into two discrete classes with respect to the stage of post-translational processing at which the block occurs. In all cases the mutant glycoproteins are inserted normally into the endoplasmic reticulum membrane, receive the two-high-mannose oligosaccharides, and apparently lose the NH2-terminal signal sequence of 16 amino acids. In cells infected with one class of mutants, no further processing of the glycoprotein occurs, and we conclude that the mutant protein is blocked at a pre-Golgi stage. In cells infected with ts L511(V), however, addition of the terminal sugars galactose and sialic acid occurs normally. Thus the maturation of G proceeds through several Golgi functions but is blocked before its appearance on the cell surface. The oligosaccharide chain of ts L511(V) G, accumulated at either the permissive (where surface maturation occurs) or the nonpermissive temperature, lacks one saccharide residue, probably fucose. In addition, no fatty acid residues are added to the ts L511(V) G protein at the nonpermissive temperature, although addition does occur under permissive conditions. 相似文献
107.
Richard H. Porter Sahli A. Cavallaro John D. Moore 《Ethology : formerly Zeitschrift fur Tierpsychologie》1980,53(2):153-170
Developmental parameters of mother-infant interactions in Acomys cahirinus were investigated in a series of observational and experimental studies. The uniquely precocial offspring associated closely with both parents beyond the time of weaning and birth of the next litter. The survival rate of foster pups was dependent upon both the age of the pups and the physiological stare of the foster mothers. While 1 and 8-day post partum ♂♂ nursed unfamiliar neonates as frequently as their own pups, they interacted with unfamiliar 8-day-old offspring less than with their own. 相似文献
108.
S C Suffin G A Prince K B Muck D D Porter 《Journal of immunology (Baltimore, Md. : 1950)》1979,123(1):10-14
Infant ferrets can be protected from respiratory syncytical virus challenge at 3 days of age by gestational infection of their mothers. Ferrets acquire their immunity to respiratory syncytial virus postpartum via immunizing products of lactation. The level of protection against viral replication correlates with the maternal serum neutralizing titer or a concomitant factor. Passive administration of adult ferret serum with a neutralizing titer of 1:1024 or greater, either i.p. or orally does not confer immunity. A nonantibody-mediated protective mechanism appears to play an important role in protecting the infant ferret from respiratory syncytial virus replication. Our findings allow the testing of the efficacy of future human vaccines before human clinical trial. 相似文献
109.
Immunoreactive vasoactive intestinal polypeptide (VIP) was present in portal hypophyseal blood of 24 male rats in concentrations (mean, 995 pg per ml) that were approximately 19 times as high as those in systemic arterial blood (mean, 52 pg per ml). The results demonstrate release of VIP from the hypothalamic-neurohypophyseal complex into the portal circulation, and establish a mechanism for direct influence of the peptide on pituitary function. 相似文献
110.
Amino acid sequence around the thiol and reactive acyl groups of human complement component C4. 总被引:12,自引:4,他引:8
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Activation of the fourth component of complement (C4) by C1s results in the generation of a reactive acyl group, able to react with putrescine, and in the release of a free thiol group that cannot be detected in the native haemolytically active molecule. Both the reactive acyl group and the free thiol group have been shown to reside in C4d, a fragment of the alpha'-chain of C4b derived from digestion of the molecule with the control proteins C3b inactivator and C4-binding protein. Peptides derived from CNBr digestion of [1,4-14C]putrescine-labelled and iodo(2-14C]acetic acid-labelled C4d have been obtained and used to establish a continuous sequence of 88 residues from the N-terminus of the molecule. The thiol and reactive acyl groups are contained in an octapeptide that shows near identity with the equivalent sequences reported for alpha 2-macroglobulin and C3. Other adjacent short sections also show homology of sequence between the three proteins, and it is highly likely that they contribute to the overall structure that gives a unique reactivity to the thiol ester bond postulated to exist in the native forms of the three proteins. 相似文献