全文获取类型
收费全文 | 469篇 |
免费 | 44篇 |
国内免费 | 1篇 |
专业分类
514篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 13篇 |
2015年 | 10篇 |
2014年 | 17篇 |
2013年 | 32篇 |
2012年 | 32篇 |
2011年 | 38篇 |
2010年 | 19篇 |
2009年 | 15篇 |
2008年 | 30篇 |
2007年 | 28篇 |
2006年 | 27篇 |
2005年 | 26篇 |
2004年 | 24篇 |
2003年 | 15篇 |
2002年 | 17篇 |
2001年 | 13篇 |
2000年 | 15篇 |
1999年 | 12篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 9篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1977年 | 2篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1970年 | 4篇 |
1964年 | 1篇 |
1958年 | 2篇 |
1956年 | 1篇 |
1955年 | 1篇 |
1897年 | 1篇 |
排序方式: 共有514条查询结果,搜索用时 15 毫秒
1.
2.
This study used monoclonal antibodies to sheep MHC class II molecules as well as an L cell transfectant (T8.1) which expresses DRA and DRB genes to show that two distinct DRβ chains are expressed in the sheep. Two anti-β chain specific monoclonal antibodies VPM37 and VPM43 react with DR antigen but not DQ antigen by ELISA. These two antibodies do not react with the DRβ chain expressed in the T8.1 cell line. Two-dimensional immunoblotting shows that these antibodies recognize a subgroup of the spots recognized by the DR-specific monoclonal antibody VPM57 which does react with the T8.1 β chain. Amino-terminal sequence analysis of the α chain associated with VPM37β chain shows that this α chain is homologous to the human DRα chain strongly indicating that the β chain is DR-like. VPM37 and VPM43 are shown to be directed against different epitopes on sheep MHC class II molecules so it is highly unlikely that the data can be explained by the presence of posttranslational modifications or the existence of a very common allele. These data provide clear evidence for the expression of two distinct DRP chains in the sheep. 相似文献
3.
4.
As we have seen, natural antibodies first emerged as an experimental phenomenon without a plausible theoretical explanation. They were originally denied the status of antibody; then, adjustments to the side-chain theory transformed them from a curiosity into a foundation of the theory. However, in accommodating natural antibodies, Ehrlich had opened several holes in his mechanism of antibody formation.Thus, by 1905, natural antibodies were clearly established as problematic. From the practical standpoint, it seemed unwise to maintain an identity between normal and immune antibodies, given the therapeutic differences in their avidity. With the decline of Ehrlich's theory of antibody formation and the spread of Landsteiner's hapten technique for the production of antibodies against artificial antigens after World War I, the theoretical possibility of their existence as other than anomaly seemed more remote than ever. However, outside the theory and despite clinical considerations, natural antibodies remained a perplexing experimental phenomenon.49 相似文献
5.
Evidence from morphology and anatomy (including embryology), as well as from palynology, chemistry and cytology, indicates
thatHydrastis is quite divergent from Ranunculaceae (in which the genus has been most often included) as well as from both Glaucidiaceae
and Berberidaceae. Distinctive features ofHydrastis, which demarcate it from Ranunculaceae but which are sometimes shared by Berberidaceae, are: the unique mode of origin of
the vascular supply to stamens and carpels; the micropyle being formed by both integuments; the xylem not V-shaped in cross
section; scalariform vessel perforations present; haploid chromosome number 13; pollen tectum consisting of a compound layer
of striae; leaf mesophyll not differentiated; the unique course of stem medullary bundles; D-galactose present. Its distinctive
higher haploid chromosome number, as well as its many less-specialized character states (in floral structure, leaf anatomy,
and xylem and vessel morphology), suggest thatHydrastis is a relictual primitive group which diverged early from a common ancestral stock of Ranunculaceae, Berberidaceae and probably
of Circaeasteraceae; at least some of the features shared byHydrastis and one or another of the families concerned seem to be a heritage from their common ancestor. We propose a reestablishment
of a monotypic family, Hydrastidaceae. 相似文献
6.
J. Keating L. Dratcu M. Lader R.A. Sherwood 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1993,615(2)
A reversed-phase high-performance liquid chromatographic method is described for the measurement of plasma serotonin concentrations. Sample preparation is by a simple solid-phase extraction using C18 columns. An isocratic separation is used with electrochemical detection. The application of the method to the measurement of plasma serotonin concentrations following the administration of fluvoxamine (a serotonin re-uptake inhibitor), maprotiline (a noradrenaline re-uptake inhibitor) and placebo to normal subjects for a seven-day period is reported. Fluvoxamine significantly decreases plasma serotonin over this time period in a linear fashion. No effect on plasma serotonin was seen for maprotiline or placebo. Plasma serotonin concentrations can be used to monitor compliance with fluvoxamine therapy. 相似文献
7.
T. Macedo C. A. Fontes Ribeiro D. Cotrim P. Tavares M. T. Morgadinho M. Caramona M. T. Nunes Vicente L. Rodrigues M. G. Cardoso M. L. Keating 《Molecular neurobiology》1995,11(1-3):21-29
This work evaluated in a population of heroin and heroin plus cocaine human addicts:
- Norepinephrine (NE), epinephrine (Epi), and 3-methoxy-4-hydroxyphenylglycol (MHPG) (the principal metabolite of brain NE) plasma levels;
- Monoamine oxidase (MAO) activity; and
- 3H-imipramine specific binding to the amine carrier in platelets.
8.
S T Keating J S Elkinton J P Burand J D Podgwaite C S Ferguson 《Journal of economic entomology》1991,84(4):1329-1333
DNA hybridization assays were used to detect the presence of viral DNA in gypsy moth (Lymantria dispar L.) larvae collected weekly from high density populations or reared from field-collected egg masses. DNA was extracted from larvae, bound to nitrocellulose filters, and hybridized with digoxigenin-labeled L. dispar NPV (LdNPV) DNA probes. The virus incidence determined from DNA hybridization assays was compared with that determined with conventional microscopic examination of larvae for polyhedral inclusion bodies. Among neonates reared from field-collected egg masses, average mortality from LdNPV (15.4%) within 10 d after hatch was not significantly different from the percentage of extracts containing LdNPV DNA (14.8%) found among larvae frozen 5 d after hatch before any mortality occurred. Field-collected larvae were split into two groups: half were frozen immediately and probed for LdNPV DNA and the other half were reared on artificial diet. The proportion containing LdNPV DNA closely approximated the proportion that died within 6 d of collection, but the proportion that died within 13 d of collection was underestimated. 相似文献
9.
L Banci L B Dugad G N La Mar K A Keating C Luchinat R Pierattelli 《Biophysical journal》1992,63(2):530-543
The structure of ClO4 and NO3 adducts of cobalt(II) substituted bovine carbonic anhydrase have been investigated through 1D NOE and 2D 1H nuclear magnetic resonance (NMR) spectroscopy. For the first time two-dimensional NMR techniques are applied to paramagnetic metalloproteins other than iron-containing proteins. Several active site signals have been assigned to specific protons on the grounds of their scalar and dipolar connectivities and T1 values. The experimental dipolar shifts for the protons belonging to noncoordinated residues have allowed the identification of a plausible orientation of the magnetic susceptibility tensor around the cobalt ion as well as of the magnitude and the anisotropy of the principal susceptibility values. In turn, a few more signals have been tentatively assigned on the grounds of their predicted dipolar shifts. The two inhibitor derivatives have a very similar orientation but a different magnitude of the chi tensor, and the protein structure around the active site is highly maintained. The results encourage a more extensive use of the two-dimensional techniques for obtaining selective structural information on the active site of metalloenzymes. With this information at hand, comparisons within homologous series of adducts with various inhibitors and/or mutants of the same enzyme of known structure should be possible using limited sets of NMR data. 相似文献
10.
Influence of Concanavalin A, wheat germ agglutinin, and soybean agglutinin on the fusion of myoblasts in vitro 总被引:6,自引:6,他引:0 下载免费PDF全文
Although muscle cell fusion was shown to be an energy-requiring process, release of myoblasts from an EGTA fusion block could be accomplished with Earle's balanced salt solution (containing 1.8 mM Ca++) free of glucose or any other energy-produced metabolite. The effect of concanavalin A, abrin, and the lectins from wheat germ, soybean, and Lens culinaris on myoblast fusion was examined with synchronized myoblast cultures upon release from fusion block. At a concentration of 15 mug/ml, these lectins were found to inhibit the fusion process to the extent of 62%, 41%, 32%, 8%, and 19%, respectively. Concanavalin A inhibition could be prevented by alpha-methyl-D-mannoside. The inhibitory effect of all the lectins except abrin could be reversed by changing to the normal, serum-containing medium. The number of binding sites was 3.4 X 10(7), 6.1 X 10(7), and 1.7 X 10(6), respectively. Although myoblasts were found to have about twice as many binding sites for wheat germ agglutinin as for concanavalin A, concanavalin A was determined to be twice as effective as wheat germ agglutinin as an inhibitor of myoblast fusion. These findngs raise the possibility that specific cell surface glycoproteins may be an important factor in this process. 相似文献