全文获取类型
收费全文 | 5978篇 |
免费 | 535篇 |
国内免费 | 1篇 |
出版年
2023年 | 23篇 |
2022年 | 25篇 |
2021年 | 144篇 |
2020年 | 88篇 |
2019年 | 130篇 |
2018年 | 150篇 |
2017年 | 124篇 |
2016年 | 182篇 |
2015年 | 288篇 |
2014年 | 330篇 |
2013年 | 344篇 |
2012年 | 440篇 |
2011年 | 356篇 |
2010年 | 240篇 |
2009年 | 200篇 |
2008年 | 293篇 |
2007年 | 278篇 |
2006年 | 246篇 |
2005年 | 247篇 |
2004年 | 216篇 |
2003年 | 218篇 |
2002年 | 200篇 |
2001年 | 124篇 |
2000年 | 115篇 |
1999年 | 98篇 |
1998年 | 75篇 |
1997年 | 50篇 |
1996年 | 51篇 |
1995年 | 59篇 |
1994年 | 49篇 |
1993年 | 44篇 |
1992年 | 92篇 |
1991年 | 71篇 |
1990年 | 78篇 |
1989年 | 58篇 |
1988年 | 58篇 |
1987年 | 53篇 |
1986年 | 39篇 |
1985年 | 53篇 |
1984年 | 33篇 |
1983年 | 40篇 |
1982年 | 41篇 |
1981年 | 38篇 |
1980年 | 26篇 |
1979年 | 30篇 |
1978年 | 21篇 |
1977年 | 19篇 |
1976年 | 22篇 |
1973年 | 24篇 |
1968年 | 17篇 |
排序方式: 共有6514条查询结果,搜索用时 15 毫秒
101.
The informativeness and inheritance of randomly amplified polymorphic DNA (RAPD) markers were investigated in an intraspecific F1 progeny derived from two heterozygous parents. The analysis confirmed the utility of RAPD markers for comparing candidate parents for the development of a molecular genetic map, and provided numerous markers for linkage analysis in a crop with a very limited history of classical or molecular genetic studies. Six potential parental lines (themselves F1 hybrid clones) showed between 1.82 and 0.62 segregating bands per primer in three hybrid families. Forty-three percent (309) of 722 primers produced polymorphic products in the most informative of these three crosses, revealing 328 single-dose (SD) markers segregating 1:1 for presence/absence in a progeny of 90 individuals. A second class of informative markers were those present in both parents but segregating in the progeny. Fifty-seven or 67% of the monomorphic but segregating markers exhibited the 3:1 ratio expected for SD dominant markers in a cross between heterozygotes. Linkage groups were constructed from the segregation of SD RAPD markers originating in the female (TMS 30572) and the male (CM2177-2) parent. Key words : RAPDs, molecular markers, genetic segregation, Manihot, single-dose markers. 相似文献
102.
Neuronal communication involves the fusion of neurotransmitter filled synaptic vesicles with the presynaptic terminal. This
exocytotic event depends upon proteins present in three separate compartments: the synaptic vesicle, the synaptic cytosol,
and the presynaptic membrane. Recent data indicate that the basic components of exocytotic pathways, including those used
for neurotransmitter release, are conserved from yeast to human. Genetic dissection of the secretory pathway in yeast, identification
of the target proteins cleaved by the clostridial neurotoxins and biochemical characterization of the interactions of synaptic
proteins from vertebrates have converged to provide the SNARE (soluble NSF attachment protein receptor) hypothesis for vesicle
trafficking. This model proposes that proteins present in the vesicle (v-SNAREs) interact with membrane receptors (t-SNAREs)
to provide a molecular scaffold for cytosolic proteins involved in fusion. The hypothesis that these mechanisms function at
the synapse relies largely uponin vitro evidence. Recently, genetic approaches in mice, C.elegans and the fruitfly,Drosophila melanagaster, have been used to dissect thein vivo function of numerous proteins involved in synaptic transmission. This review covers recent progress and insights provided
by a genetic dissection of neurotransmitter release inDrosophila. In addition, we will provide evidence that the mechanisms for synaptic communication are highly conserved from invertebrates
to vertebrates, makingDrosophila an ideal model system to further unravel the intricacies of synaptic transmission. 相似文献
103.
Thomas Altmann Gisela Felix Alison Jessop Annette Kauschmann Ursula Uwer Hugo Peña-Cortés Lothar Willmitzer 《Molecular genetics and genomics : MGG》1995,247(5):646-652
Using a two-component Ac/Ds system consisting of a stabilized Ac element (Acc1) and a non-autonomous element (DsA), 650 families of plants carrying independent germinal DsA excisions/transpositions were isolated. Progenies of 559 of these Acc1/DsA families, together with 43 families of plants selected for excision/transposition of wild-type (wt)Ac, were subjected to a broad screening program for mutants exhibiting visible alterations. This resulted in the identification of 48 mutants showing a wide variety of mutant phenotypes, including embryo lethality (24 mutants), chlorophyll defects (5 mutants), defective seedlings (2 mutants), reduced fertility (5 mutants), reduced size (3 mutants), altered leaf morphology (2 mutants), dark green, unexpanded rosette leaves (3 mutants), and aberrant flower or shoot morphology (4 mutants). To test whether these mutants were due to transposon insertions, a series of Southern blot experiments was performed on 28 families, comparing in each case several mutant plants with others showing the wild-type phenotype. A preliminary analysis revealed in 4 of the 28 families analyzed a common, novel DsA fragment in all mutant plants, which was present only in heterozygous plants with wt phenotype, as expected for DsA insertion mutations. These four mutants included two showing embryo lethality, one with dark green, unexpanded rosette leaves and stunted inflorescences, and one with curly growth of stems, leaves and siliques. Further evidence for DsA insertion mutations was obtained for one embryo lethal mutant and for the stunted mutant, while in case of the second embryo lethal mutant, the DsA insertion could be separated from the mutant locus by genetic recombination. 相似文献
104.
Analyses of meiotic and mitotic chromosomes were undertaken in 16 taxa of Echinocereus belonging to 12 species and all seven taxonomic sections (sensu Taylor). Chromosome numbers are reported for the first time for eight taxa, and previously published chromosome counts are confirmed for the remaining eight. Both diploid and polyploid counts were obtained. Eleven (69%) of the taxa surveyed were diploid (2n = 22); the five varieties of E. engelmannii were polyploid (2n = 44). Overall, chromosome counts are available for 23 of the 48 proposed species (sensu Taylor). Of these, 19 (82%) are diploid, and four (18%) are polyploid. Polyploid cytotypes are most common in the primitive sections, e.g., sections Erecti and Triglochidiatus, which suggests that polyploidy is probably a derived condition in Echinocereus. Polyploid taxa range from medium to high latitudes and elevations relative to the overall distribution of the genus. Polyploidy, hybridization, and cryptic chromosomal rearrangements are thought to be the major causes of the speciation events of the genus. 相似文献
105.
The effect of 12 surfactants on aflatoxin production, growth, and conidial germination by the fungus Aspergillus flavus is reported. Five nonionic surfactants, Triton X-100, Tergitol NP-7, Tergitol NP-10, polyoxyethylene (POE) 10 lauryl ether, and Latron AG-98, reduced aflatoxin production by 96 to 99% at 1% (wt/vol). Colony growth was restricted by the five nonionic surfactants at this concentration. Aflatoxin production was inhibited 31 to 53% by lower concentrations of Triton X-100 (0.001 to 0.0001%) at which colony growth was not affected. Triton X-301, a POE-derived anionic surfactant, had an effect on colony growth and aflatoxin production similar to that of the five POE-derived nonionic surfactants. Sodium dodecyl sulfate (SDS), an anionic surfactant, and dodecyltrimethylammonium bromide, a cationic surfactant, suppressed conidial germination at 1% (wt/vol). SDS had no effect on aflatoxin production or colony growth at 0.001%. The degree of aflatoxin inhibition by a surfactant appears to be a function of the length of the hydrophobic and hydrophilic chains of POE-derived surfactants. 相似文献
106.
Guerrero Francisco; Blanco Jose M; Rodriguez Valeriano 《Journal of plankton research》1994,16(1):95-103
A comparative analysis was carried out on the several equationsmost commonly used to describe the dependence of the developmentof organisms on temperature. Goodness of fit, number of parameters,ease of fitting data and biological significance were compared. 相似文献
107.
108.
C. Cafè C. Torri S. Gatti D. Adinolfi P. Gaetani R. Rodriguez Y. Baena F. Marzatico 《Neurochemical research》1994,19(12):1551-1555
Non-synaptosomal and synaptosomal mitochondrial membrane-linked enzymatic activities, NADH-cytochrome c reductase rotenone insensitive (marker of the outer membrane) and cytochrome oxidase (marker of the inner membrane), were measured in rat brain hippocampus and striatum immediately after and 1, 4, and 7 days following the induction of complete transient ischemia (15 min) by the four vessel occlusion method. Furthermore citrate synthetase activity was measured with and without Triton X-100 in order to qualitatively evaluate the membrane permeability. Nonsynaptosomal mitochondrial membranes showed reduction of both activities only in the late reperfusion phase: NADH-CCRRi decreased in striatal mitochondria after 4–7 days and only after 7 days in the hippocampus. COX activity decreased only in striatal mitochondria 7 days after ischemia. Non-synaptosomal mitochondrial membrane permeability did not show changes. Synaptosomal mitochondria showed a decrease of NADH-CCRRi only at 7 days of reperfusion both in hippocampus and striatum, while COX activity decreased only during ischemia and returned to normal levels in the following days in the two areas considered. In summary, free mitochondria showed insensitiveness to ischemia but they risulted damaged in the late reperfusion phase, while mitochondria from the synaptic terminal showed ischemic damage, partially restored during reperfusion. The striatal mitochondria showed a major susceptibility to ischemia/repefusion damage, showing changes earlier than the hippocampal ones. 相似文献
109.
Summary Embryogenic cultures were initiated from immature pecan zygotic embryos. Explants were induced for one week on Woody Plant Medium with either -naphthaleneacetic acid or 2,4-dichlorophenoxyacetic acid at 2, 6 or 12 mg/l, then subcultured monthly to fresh basal medium. Observations were made on callus production, embryo formation, and embryo morphology. Somatic embryo morphology and overall callus proliferation were affected by auxin type. Callus proliferation was less extensive and more somatic embryos resembling zygotic embryos were obtained from cultures initiated with -naphthaleneacetic acid than with 2,4-dichlorophenoxyacetic acid. Repetitive somatic embryogenesis was obtained in all auxin treatments. Conversion into plantlets was affected by somatic embryo morphology in that embryos with poorly developed apices exhibited lower percentages of conversion than those with well developed single or multiple apices. Consequently, although more embryos were obtained with 2,4-dichlorophenoxyacetic acid, naphthaleneacetic acid was the superior auxin for production of somatic embryos more likely to convert into plants.Abbreviations BAP
6-benzylaminopurine
- IAA
indole-3-acetic acid
- IBA
indole-3-butyric acid
- NAA
-naphthaleneacetic acid
- 2,4-D
2,4-dichlorophenoxyacetic acid
- WPM
Woody Plant Medium (Lloyd & McCown 1980) 相似文献
110.
Rodriguez Maria E. Hozbor Daniela F. Samo Analia L. Ertola Rodolfo Yantorno Osvaldo M. 《Journal of industrial microbiology & biotechnology》1994,13(5):273-278
Summary The kinetics ofBordetella pertussis growth was studied in a glutamate-limited continuous culture. Growth kinetics corresponded to Monod's model. The saturation constant and maximum specific growth rate were estimated as well as the energetic parameters, theoretical yield of cells and maintenance coefficient. Release of pertussis toxin (PT) and lipopolysaccharide (LPS) were growth-associated. In addition, they showed a linear relationship between them. Growth rate affected neither outer membrane proteins nor the cell-bound LPS pattern.Nomenclature X
cell concentration (g L–1)
-
specific growth rate (h–1)
- m
maximum specific growth rate (h–1)
- D
dilution rate (h–1)
- S
concentration of growth rate-limiting nutrient (glutamate) (mmol L–1 or g L–1)
- Ks
substrate saturation constant (mol L–1)
- ms
maintenance coefficient (g g–1 h–1)
- Yx/s
theoretical yield of cells from glutamate (g g–1)
- Yx/s
yield of cells from glutamate (g g–1)
- YPT/s
yield of soluble PT from glutamate (mg g–1)
- YKDO/s
yield of cell-free KDO from glutamate (g g–1)
- YPT/x
specific yield of soluble PT (mg g–1)
- YKDO/x
specific yield of cell-free KDO (g g–1)
- qPT
specific soluble PT production rate (mg g–1 h–1)
- qKDO
specific cell-free KDO production rate (g g–1 h–1) 相似文献