全文获取类型
收费全文 | 78868篇 |
免费 | 6547篇 |
国内免费 | 4891篇 |
专业分类
90306篇 |
出版年
2024年 | 139篇 |
2023年 | 901篇 |
2022年 | 2079篇 |
2021年 | 3605篇 |
2020年 | 2327篇 |
2019年 | 2840篇 |
2018年 | 2873篇 |
2017年 | 2032篇 |
2016年 | 2873篇 |
2015年 | 4587篇 |
2014年 | 5297篇 |
2013年 | 5965篇 |
2012年 | 6897篇 |
2011年 | 6355篇 |
2010年 | 3818篇 |
2009年 | 3376篇 |
2008年 | 4113篇 |
2007年 | 3655篇 |
2006年 | 3172篇 |
2005年 | 2684篇 |
2004年 | 2279篇 |
2003年 | 1972篇 |
2002年 | 1730篇 |
2001年 | 1559篇 |
2000年 | 1565篇 |
1999年 | 1447篇 |
1998年 | 847篇 |
1997年 | 799篇 |
1996年 | 808篇 |
1995年 | 737篇 |
1994年 | 687篇 |
1993年 | 530篇 |
1992年 | 818篇 |
1991年 | 657篇 |
1990年 | 601篇 |
1989年 | 531篇 |
1988年 | 421篇 |
1987年 | 362篇 |
1986年 | 336篇 |
1985年 | 299篇 |
1984年 | 221篇 |
1983年 | 199篇 |
1982年 | 112篇 |
1981年 | 118篇 |
1980年 | 86篇 |
1979年 | 147篇 |
1978年 | 84篇 |
1977年 | 95篇 |
1975年 | 111篇 |
1974年 | 116篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
本文报道在我国广西隆林壮族中发现一个罕見的HbQ复合α,β地中海贫血家系。先证者女,18岁,贫血面容,肝脾肿大。化学结构分析确证本Hb变异体为HbQ Thailand[α74(EF3)Asp→His]。血红蛋白组成以及α和β珠蛋白基因分析结果表明,先证者的珠蛋白基因型为-α~Q/-α~T复合β°/β°(IVSI-1G→T/Codon17A→T);先证者父的基因型为-‘α~Q/-复合β~O/β~A(IVSI-1G→T/β~A);先证母的基因型为-α~T/αα复合β~O/β~A(Codon17A→T/β~A)。 相似文献
82.
Mu-jin Tang Shao-ling Zeng Jian-wu Chen Yong-xia Shi Wei Xu Mei-jin Yuan Yi Pang 《Insect Science》2003,10(4):221-229
A series of plasmids were constructed to examine the effects of p19 and orf1‐orf2 genes from Bacillus thuringiensis on Cyt1Aa synthesis and inclusion formation. The plasmids expressed the cyt1Aa gene along with either p19 or orf1‐orf2, or each of them coordinatively with p20 in the acrystalliferous strain of B. thuringiensis subsp. israelensis 4Q7. No effect on the expression of Cyt1Aa protein was found when P19 or Orf1‐Orf2 co‐expressed with Cyt1Aa. However, when including p20 gene, the constructs with p19 or orf1‐orf2 gene produced lower yield of Cyt1Aa proteins than without p19 or orf1‐orf2 gene. Electron microscopy observation and bioassay showed that P19 and Orf1‐Orf2 have no influence on the crystal size and toxicity of Cyt1Aa protein. It is presumed that P19 and Orf1‐Orf2 might have negative effects on Cyt1Aa synthesis in B. thuringiensis. 相似文献
83.
Morphometric Analysis of Hepatocellular carcinomaLaiMao-de(来茂德);ChenPei-hui(陈培辉)andZhouShui-yun(周水云)(DepartmentofPathology,Zh... 相似文献
84.
Atelocauda koae, a rust of the native HawaiianAcacia koa, is considered as a demicyclic species, having spermogonial, aecial, and telial states, but is unusual in production of aeciospores
simultaneously with teliospores rather than consecutively. Host inoculation with spores of each state separately confirmed
that the life cycle was perpetuated by the telial state, but the aeciospores, while capable of germination and stomal penetration,
did not produce detectable infection. This rust therefore behaves as a microcyclic species, and appears to be in evolutionary
transition toward this reduced state. Teliospores produced vestigial, permanently attached basidiosopores which germinated
to produce infective hyphae. The hyphae entered the host either through stomata or penetrated the epidermis directly, with
the latter method being more common. Unusual nuclear associated with teliospore germination, in which meiosis occurs in more
than one diploid nucleus was observed, in confirmation of an earlier study. 相似文献
85.
A gene encoding a truncated large subunit of Rubisco is transcribed and salt-inducible in rice 总被引:16,自引:0,他引:16
J.-S. Zhang J. Gu F.-H. Liu S.-Y. Chen 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1995,91(2):361-366
Using the rice salt-tolerant mutant 20 as material, a cDNA library was constructed and two salt-inducible clones, SIR5.5 and SIR8.1, were isolated by differential screening. Homology analysis revealed that the two clones together constituted a chimeric rbcL which encoded a truncated large subunit of Rubisco with 337 amino-acids, plus 64 amino-acids of unknown origin. The expressions of both the normal and the chimeric locus appeared to be developmentally regulated and salt-inducible in shoots of the salt-tolerant mutant 20 and its original variety 77–170. In roots, their expressions were salt-inducible in the salt-tolerant mutant 20 whereas no, or only premature, forms were present in the salt-treated original variety 77–170. Higher concentrations of salt reduced the expressions of both normal rbcL and the chimeric locus. ABA showed no effect on their expression. 相似文献
86.
W. L. Li P. D. Chen L. L. Qi D. J. Liu 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1995,90(3-4):526-533
A species-specific repeated sequence, pHvNAU62, was cloned from Haynaldia villosa, a wheat relative of great importance. It strongly hybridized to H. villosa, but not to wheat. In situ hybridization localized this sequence to six of seven H. villosa chromosome pairs in telomeric or sub-telomeric regions. Southern hybridization to whea-H. villosa addition lines showed that chromosomes 1V through 6V gave strong signals in ladders while chromosome 7V escaped detection. In addition to H. villosa, several Triticeae species were identified for a high abundance of the pHvNAU62 repeated sequence, among which Thinopyrum bassarabicum and Leymus racemosus produced the strongest signals. Sequence analysis indicated that the cloned fragment was 292 bp long, being AT rich (61%), and showed 67% homology of pSc7235, a rye repeated sequence. Isochizomer analysis suggested that the present repeated sequence was heavily methylated at the cytosine of the CpG dimer in the genome of H. villosa.It was also demonstrated that pHvNAU62 is useful in tagging the introduced 6VS chromosome arm, which confers a resistance gene to wheat powdery mildew, in the segregating generations. 相似文献
87.
J S Modica-Napolitano M J Weiss L B Chen J R Aprille 《Biochemical and biophysical research communications》1984,118(3):717-723
Rhodamine 123 accumulates in the mitochondria of living cells and exhibits selective anticarcinoma activity. The biochemical basis of toxicity was investigated by testing the effect of the dye on isolated rat liver mitochondria. Much lower concentrations of rhodamine 123 were required to inhibit ADP-stimulated respiration and ATP synthesis in well-coupled energized mitochondria than were required to inhibit uncoupled respiration and uncoupler-stimulated ATP hydrolysis. The amount of rhodamine 123 associated with the mitochondria was several-fold greater under energized as compared to non-energized conditions, which may explain why coupled functions appeared to be more sensitive than uncoupled functions to inhibition at low concentrations of rhodamine 123. It was concluded that the site of rhodamine 123 inhibition is most likely the F0F1 ATPase complex and possibly electron transfer reactions as well. 相似文献
88.
When LETS protein positive and negative cells were co-cultured, the positive cells remained as positive and the negative cells remained as negative. Apparently the transformed cells do not secrete factors which are sufficient to influence the distribution of surface LETS protein on normal cells. 相似文献
89.
Precise and quantitative reversed-phase high performance liquid chromatographic (HPLC) procedures are described which can be used in biogenic amine and neuropeptide research. The amine procedure was applied to various pharmacological matrices including plasma, heart tissue and brain. The use of peptide HPLC as an analytical tool for various neuropeptides is illustrated by studies on des-tyrosine-gamma-endorphin (DT gamma E) metabolism in the brain and the stability of an ACTH (ORG-2766) analogue during a chronic infusion in rats. The power of HPLC as a research tool in peptide pharmacology is described, discussed and demonstrated as an aid in the understanding of the pharmacological effects of exogenous peptides and the function of the brain. 相似文献
90.
Decreased uptake and retention of rhodamine 123 by mitochondria in feline sarcoma virus-transformed mink cells 总被引:6,自引:0,他引:6
A reduce uptake and retention of the mitochondria-specific membrane potential probe rhodamine 123 by feline sarcoma virus (FeSV)-transformed mink fibroblasts (64F3) has been detected. The decreased accumulation of rhodamine 123 by 64F3 mitochondria is not due to abnormal plasma membrane dye permeability, since after microinjection of the dye these cells are still unable to retain the dye at levels comparable to the untransformed parental cells, CCL 64. Nigericin, an ionophore that mediates an electrically neutral exchange of protons for potassium ions resulting the elimination of the pH gradient across the mitochondrial membrane and a compensatory increase in mitochondrial membrane potential with continued respiration, increases both the dye uptake and the retention time in transformed 64F3 cells. These results suggest that mitochondria in FeSV-transformed mink cells may have an abnormally low mitochondrial membrane potential accompanied by a relatively high pH gradient. Since anioic metabolites such as pyruvate and glutamate are accumulated by mitochondria in proportion to the delta pH across the mitochondrial membrane, the abnormal mitochondria described here may contribute to the abnormal metabolic state of FeSV-transformed cells. 相似文献