全文获取类型
收费全文 | 793488篇 |
免费 | 85507篇 |
国内免费 | 352篇 |
专业分类
879347篇 |
出版年
2018年 | 7018篇 |
2016年 | 9493篇 |
2015年 | 12846篇 |
2014年 | 14953篇 |
2013年 | 21538篇 |
2012年 | 23907篇 |
2011年 | 24386篇 |
2010年 | 16782篇 |
2009年 | 15467篇 |
2008年 | 22000篇 |
2007年 | 23081篇 |
2006年 | 21598篇 |
2005年 | 20582篇 |
2004年 | 20638篇 |
2003年 | 19714篇 |
2002年 | 19383篇 |
2001年 | 31409篇 |
2000年 | 31470篇 |
1999年 | 25370篇 |
1998年 | 9497篇 |
1997年 | 9899篇 |
1996年 | 9352篇 |
1995年 | 8821篇 |
1994年 | 8579篇 |
1993年 | 8731篇 |
1992年 | 21908篇 |
1991年 | 21505篇 |
1990年 | 21305篇 |
1989年 | 20790篇 |
1988年 | 19775篇 |
1987年 | 18755篇 |
1986年 | 17588篇 |
1985年 | 17918篇 |
1984年 | 14955篇 |
1983年 | 12856篇 |
1982年 | 10052篇 |
1981年 | 8985篇 |
1980年 | 8627篇 |
1979年 | 14331篇 |
1978年 | 11333篇 |
1977年 | 10534篇 |
1976年 | 10068篇 |
1975年 | 10835篇 |
1974年 | 12117篇 |
1973年 | 11834篇 |
1972年 | 10975篇 |
1971年 | 9972篇 |
1970年 | 8721篇 |
1969年 | 8668篇 |
1968年 | 8213篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
G. Zosimo-Landolfo 《Bio Tribune Magazine》2007,24(1):50-51
Syphilis serology must be determined in pregnant women during the first prenatal visit. An economic analysis of the serological tests used in Thailand indicates that combined VDRL and TPHA testing is the most cost-effective screening protocol. It represents an optimal alternative for systematic screening in that country. 相似文献
982.
The morphology of dissociated single cerebellar Purkinje cells obtained from wild-type P1 CD1 mice was assessed in the absence
and in the presence of glia. A dedicated noninvasive technique based on optical microscopy was developed. Image processing
algorithms were implemented to extract metrical features characterizing cell structure and dendritic arborization. The morphological
features were analyzed in order to identify quantitative differences in Purkinje cell morphology due to interactions with
astrocytes. 相似文献
983.
984.
The status of the reproductive system is investigated in five species of Teleostei from the Teterev River and the Kiev Reservoir
(Ukraine), descendants of F42–F7 generations of fish exposed to radiation from the accident at the Chernobyl nuclear power plant. Twenty years after the accident,
a wide range of morphofuinctional anomalies of this system is present in fish. The most significant of them are: asymmetry
and anomalous morphology of gonads, proliferation of connective tissue—sterilization, mass destruction of follicular and sex
cells of various developmental stages, and hermaphroditism. Among the investigated species, disturbances of reproductive glands
were preset to the highest extent in pike Esox lucius and crucian carp Carassius carassius. In the series of investigated generations the maximum frequency of occurrence of gonad anomalies was noted in F4 and F5, due to prolonged mutagenesis (Dubinin, 1986). 相似文献
985.
E Karnaukhova W M Niessen U R Tjaden J Raap J Lugtenburg J van der Greef 《Analytical biochemistry》1989,181(2):271-275
In order to develop direct methods for determining the extent of metabolic incorporation of isotopically labeled amino acids into a protein, the determination of deuterated tryptophan in [2H5]tryptophan-bacteriorhodopsin was investigated. The isotopically modified protein was subjected to alkaline hydrolysis. After phenyl isothiocyanate derivatization of the hydrolysate, the mixture was separated by reversed-phase liquid chromatography. Field desorption mass spectrometry and thermospray mass spectrometry were investigated for their ability to determine the ratio between [2H5]tryptophan and total tryptophan in the collected fractions. In order to check the procedure a set of known tryptophan/[2H5]tryptophan mixtures were passed through the same derivatization, HPLC separation, and lyophilization procedure as used for the biological samples. 相似文献
986.
A method using liquid chromatography - atmospheric pressure chemical ionisation mass spectrometry was evaluated for determining the molecular species composition of phospholipids (phosphatidylcholines from soybean, egg yolk and bovine liver) after conversion to diacylglycerol nicotinate derivatives. The structures could be deduced from pseudo-molecular ions ([MH-123](+)) and three pairs of monoacyl containing fragment ions. All molecular species in mixed peaks were readily identified and many minor components, earlier not encountered in the samples under investigation, were identified. Acyl chain regioisomers were readily distinguished by the ratio of the [MH-RCHCO](+) ions. Molecular species differing only in the position of the double bonds in one polyunsaturated acyl chain were separated on the basis of retention times. A half quantitative estimation of the molecular species composition of complex samples was achieved by a combination of UV detection and, for mixed peaks, the areas of [MH-123](+) ions. 相似文献
987.
988.
Gradually altered synthetic entities were employed as molecular probes, and arachidonic acid, ADP, human alpha-thrombin and the Ca2+ ionophore A23187 as aggregation-inducing agents, in a comprehensive study on the response profile of human blood platelets with an emphasis on the effects of exogenous and increased intracellular Ca2+. Corroborating further previous conclusions, some representative carbamoylpiperidine derivatives, at concentrations effecting substantial inhibition of ADP-induced aggregation, failed to retain that effect when 5.0 mM Ca2+ was introduced into the otherwise identical test medium; reference compounds chlorpromazine and propranolol registered corresponding inhibitory patterns. At increased concentrations the compounds' inhibitory potency was regenerated even in the presence of 5 mM Ca2+. In fact, in sufficiently high concentrations, the compounds were even capable of inhibiting aggregation elicited by 15 microM of the ionophore A23187; so did chlorpromazine and propranolol. Another set of congeners revealed the striking sensitivity of ionophore A23187-induced human blood platelet aggregation to the surface active potencies of inhibitor molecules. The loss in inhibitory potency was directly related to the lesser hydrophobic character of the molecule. 相似文献
989.
Phosphate activated glutaminase in synaptosomal enriched preparation from rat brain is very sensitive to inhibition by low concentration of glutamate, ammonia and 2-oxoglutarate when added to the incubation medium at pH 7.6. By increasing the concentration of either of these compounds up to 0.5 mM a pronounced initial inhibition is followed by little or no further effect when the concentration is increased beyond this level. By lowering the pH of the reaction mixture to 7.0, the inhibition by glutamate is almost abolished and that of ammonia reduced. Glutamate inhibits mainly the N-ethylmaleimide-sensitive fraction of glutaminase which previously is suggested to be localized to the outer phase of the mitochondrial inner membrane, whereas ammonia inhibits both the N-ethylmaleimidesensitive and-insensitive fraction. Evidence has been produced to show that the inhibition by 2-oxoglutarate is caused by glutamate formation by aminotransferase reactions. Since 2-oxoglutarate is produced by the tricarboxylic acid cycle, the operation of this cycle may regulate the glutaminase reaction by controlling glutamate formation via the aminotransferase reactions.Abbreviations used NEM
N-ethylmaleimide
- PAG
phosphate activated glutaminase
- AOA
aminooxyacetic acid 相似文献
990.
E C Chew 《Acta anatomica》1980,108(2):156-159
Tannic acid was found to fix and stain glycocalyx heavily. After removal of the major component of surface glycopeptides by trypsin, the surface coat was stained vaguely, and after the treatment with collagenase, the surface coat was moderately stained. It is concluded that tannic acid stained non-specific surface glycopeptides. 相似文献