全文获取类型
收费全文 | 9600篇 |
免费 | 1070篇 |
国内免费 | 5篇 |
专业分类
10675篇 |
出版年
2022年 | 66篇 |
2021年 | 83篇 |
2018年 | 88篇 |
2017年 | 71篇 |
2016年 | 161篇 |
2015年 | 251篇 |
2014年 | 308篇 |
2013年 | 425篇 |
2012年 | 498篇 |
2011年 | 464篇 |
2010年 | 346篇 |
2009年 | 324篇 |
2008年 | 517篇 |
2007年 | 536篇 |
2006年 | 468篇 |
2005年 | 469篇 |
2004年 | 492篇 |
2003年 | 503篇 |
2002年 | 415篇 |
2001年 | 186篇 |
2000年 | 152篇 |
1999年 | 163篇 |
1998年 | 144篇 |
1997年 | 96篇 |
1996年 | 113篇 |
1995年 | 94篇 |
1994年 | 108篇 |
1993年 | 117篇 |
1992年 | 153篇 |
1991年 | 123篇 |
1990年 | 132篇 |
1989年 | 131篇 |
1988年 | 99篇 |
1987年 | 113篇 |
1986年 | 122篇 |
1985年 | 136篇 |
1984年 | 117篇 |
1983年 | 111篇 |
1982年 | 121篇 |
1981年 | 93篇 |
1980年 | 91篇 |
1979年 | 113篇 |
1978年 | 86篇 |
1977年 | 94篇 |
1976年 | 69篇 |
1975年 | 72篇 |
1974年 | 93篇 |
1973年 | 81篇 |
1972年 | 71篇 |
1970年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
P. A. Anderson G. J. Lawrence A. Pryor 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1992,84(7-8):845-850
Summary Random cDNA sequences synthesized from poly A+ RNA extracted from germinated urediospores of the flax rust fungus, Melampsora lini, were used as probes to detect restriction fragment length polymorphisms (RFLPs) in three races of M. lini originating from cultivated flax, Linum usitatissimum, and one race originating from Australian native flax, L. marginale. Fourteen out of 22 probes tested detected RFLPs in the three races from cultivated flax while 19 of the probes detected polymorphisms between these three races and the race from L. marginale. The segregation of seven RFLPs was determined in a family of 19 F2 progeny derived from a cross between two of the rust races. With six of these the inheritance was consistent, in each case, with the segregation of alleles at a single locus. Inheritance of the seventh was unusual and an explanation involving two loci with null alleles at each was proposed. No linkage was detected between any of the RFLP loci and nine unlinked loci specifying avirulence. 相似文献
82.
Lawrence W. Solomon 《The Yale journal of biology and medicine》1992,65(5):537-Oct;65(5):537
83.
We develop a multitype branching-process model for the Polymerase Chain Reaction (PCR). We apply the model to a comparison
of three methods for estimating the initial number of molecules of target present in a PCR. These three methods are: one which
uses a coamplified, internal control; one which uses an external control series; and one which uses simple extrapolation of
log outputvs time (no control). We identify assumptions for each method which permit mathematical analysis of bias and precision. All
three methods perform well if: (1) replication efficiencies are stable among reactions; (2) other method-specific conditions
on efficiencies are met; and (3) product accumulates exponentially throughout the range where it is observed. When replication
efficiencies vary among reactions but other optimal conditions for each method hold, the no-control and external-control methods
lose precision relative to the internal control method, but they may still perform satisfactorily for many applications. The
internal control method continues to perform well even if accumulation of product plateaus. This method depends, however,
on a condition we call equivalence of replication efficiencies, the attainability of which in practice remains to be proven. 相似文献
84.
85.
Characterization of the locomotor depression produced by an A2-selective adenosine agonist 总被引:2,自引:0,他引:2
Adenosine analogs, such as N6-cyclohexyladenosine (CHA) that are selective for A1-adenosine receptors, and analogs, such as 5'-N-ethylcarboxamidoadenosine (NECA) that are active at both A1 and A2 receptors, cause a profound depression of locomotor activity in mice via a central mechanism. The depression is effectively reversed by non-selective adenosine antagonists such as theophylline. We report that 2-([2-aminoethylamino) carbonylethylphenylethylamino]-5'-N-ethylcarboxamidoadenosine (APEC), an amine derivative of the A2-selective agonist, CGS21680, is a potent locomotor depressant in mice. The in vivo pharmacology is consistent with A2-selectivity at a central site of action. Two parameters indicative of locomotor activity, horizontal activity and total distance travelled, were measured using a computerized activity monitor. From dose-response curves it was found that APEC (ED50 16 micrograms/kg) is more potent than CHA (ED50 60 micrograms/kg) and less potent than NECA (ED50 2 micrograms/kg). The locomotor depression by APEC was reversible by theophylline, but not by the A1-selective antagonists 8-cyclopentyltheophylline (CPT) and 8-cyclopentyl-1, 3-dipropyl-2-thioxanthine, nor by the peripheral antagonists 8-p-sulfophenyltheophylline (8-PST) and 1,3-dipropyl-8-p-sulfophenylxanthine. The locomotor activity depression elicited by NECA and CHA was reversed by A1-selective antagonists. These results suggest that the effects of APEC are due to stimulation of A2 adenosine receptors in the brain. 相似文献
86.
A Q Sun K U Yüksel T M Jacobson R W Gracy 《Archives of biochemistry and biophysics》1990,283(1):120-129
Previously undetected isoforms of human glucose-6-phosphate isomerase (GPI) have been isolated utilizing substrate-induced elution of the enzyme from spherical cross-linked phosphocellulose as an affinity ligand and subjected to a series of physical and chemical studies. The two major isoforms (1, 48%, pI 9.13; 2, 36%, pI 9.00) are homodimers of subunits of 63.2 kDa (Type-A) and are charge isomers, probably representing deamidation of specific Asn-Gly sequences as in other species. Isoform 3 (13%, pI 8.84) is a heterodimer composed of the Type-A subunit and a previously unreported larger subunit of 69.8 kDa (Type-B). Isoform 4 (3%, pI 8.62) is a BB-homodimer. Structural differences in the two types of subunits are also apparent from CNBr fragmentation patterns. Carbohydrate analyses show that, even though potential N- and O-linked glycosylation sites exist, the isoforms are not due to glycosylation. Recently recognized sequence similarities between GPI and the neurotropic lymphokine, neuroleukin (NLK) suggest that GPI and NLK are either derived from the same gene or represent modifications of the same protein. The possibility of NLK-GPI dimers exists, but the new isoforms identified in this study do not appear to represent hybrids of GPI subunits with mature NLK. 相似文献
87.
Poly(ADP-ribose) has a branched structure in vivo 总被引:2,自引:0,他引:2
H Juarez-Salinas V Levi E L Jacobson M K Jacobson 《The Journal of biological chemistry》1982,257(2):607-609
We have searched for the presence of branching in the chromosomal polymer poly(ADP-ribose) as it occurs in vivo. Treatment of the polymer with phosphodiesterase asnd phosphomonoesterase results in the conversion of internal residues to the nucleoside ribosyladenosine and the conversion of points of branching to diribosyladenosine. We have detected diribosyladenosine in digests of the polymer derived from carcinogen-treated SV40 virus-formed 3T3 cells and in normal rat liver, kidney, and spleen. The frequency of residues involved in branching varied from 0.8 to 1.6 mole % over a 50-fold range of total levels of poly(ADP-ribose). Thus, branching seems to be a general feature of poly(ADP-ribose) as it occurs in vivo. 相似文献
88.
Glycogen, trehalose, glucose, and total lipid contents of six nematode species were studied. Anhydrobiotic Anguina tritici and Ditylencbus dipsaci stored trehalose in preference to glycogen and only small amounts of glucose were detected. Glycogen content was also reduced in anhydrobiotic Aphelenchus avenae. Conversely, Panagrellus redivivus and Turbatrix aceti contained large amounts of glycogen, appreciable amounts of glucose, and minimal amounts of trehalose. Ditylenchus myceliophagous "curds" contained low amounts of glycogen and very little trehalose; total lipid was 60% of that in fresh samples. The lipid contents of fresh samples of P. redivivus, T. aceti, and A. avenae were high (23.1, 21.9, and 36.7% dry weight, respectively), but in anhydrobiotic A. avenae larvae the level was reduced by over 60%. In contrast, lipid levels remained high in anhydrobiotic A. tritici and D. dipsaci larvae (40.6 and 38.3%, respectively). Analysis of lipid composition in anhydrobiotic A. tritici and A. avenae did not indicate any specific metabolic adaptations to desiccation survival. 相似文献
89.
90.