全文获取类型
收费全文 | 9296篇 |
免费 | 571篇 |
国内免费 | 477篇 |
出版年
2024年 | 27篇 |
2023年 | 138篇 |
2022年 | 206篇 |
2021年 | 224篇 |
2020年 | 254篇 |
2019年 | 272篇 |
2018年 | 322篇 |
2017年 | 212篇 |
2016年 | 238篇 |
2015年 | 265篇 |
2014年 | 456篇 |
2013年 | 573篇 |
2012年 | 279篇 |
2011年 | 421篇 |
2010年 | 361篇 |
2009年 | 485篇 |
2008年 | 483篇 |
2007年 | 511篇 |
2006年 | 484篇 |
2005年 | 422篇 |
2004年 | 364篇 |
2003年 | 299篇 |
2002年 | 314篇 |
2001年 | 216篇 |
2000年 | 157篇 |
1999年 | 193篇 |
1998年 | 211篇 |
1997年 | 155篇 |
1996年 | 190篇 |
1995年 | 156篇 |
1994年 | 176篇 |
1993年 | 108篇 |
1992年 | 121篇 |
1991年 | 116篇 |
1990年 | 91篇 |
1989年 | 90篇 |
1988年 | 69篇 |
1987年 | 76篇 |
1986年 | 69篇 |
1985年 | 65篇 |
1984年 | 93篇 |
1983年 | 74篇 |
1982年 | 79篇 |
1981年 | 61篇 |
1980年 | 61篇 |
1979年 | 34篇 |
1978年 | 13篇 |
1976年 | 15篇 |
1975年 | 12篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
鉴定了小伞山羊草(Ae.umbellulata)6条染色体的中国春添加系对T型细胞质雄性不育系育性的影响,发现UAD能较好地恢复T型不育系的育性,表明染色体A上携带有育性恢复基因。添加染色体A在提莫菲维细胞质背景中通过雄配子的传递率为15.6%。同时进一步证明中国春不含有恢复基因。 在体细胞染色体数为42的331个不育系与UAD的杂种衍生后代中选到18个可育株,并对部分植株进行了细胞学鉴定。其中040-5、061-1和061-4与中国春的杂种F_1的育性分离和染色体配对情况表明它们是含有来自小伞山羊草染色体A上的恢复基因的杂合易位系。 相似文献
102.
J. J. M. Meulenberg W. A. M. Loenen E. Sellink P. W. Postma 《Molecular & general genetics : MGG》1990,220(3):481-484
Summary A generally applicable method is described for reintroduction of mutant plasmid-borne alleles to the chromosome of Klebsiella pneumoniae using bacteriophage . We, used this method to make stable chromosomal transposon insertions in genes for biosynthesis of pyrroloquinoline quinone in K. pneumoniae 相似文献
103.
Lisette Waits Stephanie Dunkle F. E. Wilkinson P. Moreau Keri Safranski T. Reust Dorothy M. Morré D. J. Morré 《Protoplasma》1990,154(1):8-15
Summary Transfer of radiolabeled lipids from dictyosome-like structures (DLS) from testis tubules of the guinea pig as donor to unlabeled plasma membrane from testis tubules immobilized on nitrocellulose as acceptor was studied in a completely cell-free system. As a general label for lipids of the donor DLS, isolated testis tubules were incubated with [14C]acetate. Time- and temperature-dependent transfer of [14C]acetate labeled constituents was observed in the cellfree system. However, despite the fact that phospholipids and other constituents were highly labeled in the donor fraction, primarily radioactive sterols were transferred to the plasma membrane acceptor vesicles. Transfer at 37°C represented 0.4 to 0.7% of the total radiolabeled cholesterol at 37°C but little or no transfer occurred at 4°C. The sterols transferred exhibited Chromatographic mobilities corresponding to those of cholesterol and lanosterol. Similar results were obtained with [14C]mevalonic acid. In subsequent experiments, cholesterol transfer from DLS to plasma membrane was demonstrated by incubation of DLS with [3H]squalene which was converted into sterol or with [14C]cholesterol. Transfer of sterols required ATP, but not cytosol, and was both time- and temperature-dependent. DLS were more effective than either endoplasmic reticulum or plasma membrane as the donor fraction. The results from the cell-free analysis suggest a possible functional role of the DLS in sterol biogenesis and transfer to the plasma membrane during spermatid development.Abbreviations DLS
dictyosome-like structure(s)
- PBS
phosphatebuffered saline
- HEPES
4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- BSA
bovine serum albumin 相似文献
104.
F. Köhler I. Benediktsson G. Cardon C. S. Andreo O. Schieder 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1990,79(5):679-685
Summary In P. hybrida and B. nigra an enhancement of transformation rates (direct gene transfer) of about six to seven-fold was obtained after irradiation of protoplasts with 12.5 Gy (X-ray). The effect of protoplast irradiation was similar in experiments where protoplasts were irradiated 1h before transformation (X-ray/DNA) or 1h after completion of the transformation procedure (DNA/X-ray). Increased X-ray doses up to 62.5 Gy resulted in further enhancement of percentages of transformed colonies, indicating a correlation between relative transformation frequencies (RTF) and the doses applied. Estimation of degradation rates of plasmid sequences in plant protoplasts yielded a reduction of plasmid concentration to 50% 8–12 h after transformation. In 1-day-old protoplasts, the level of plasmid fragments dropped to 0%–10% compared to 1h after transformation. The results demonstrate that the integration rates of plasmid sequences into the plant genome may in part be governed by DNA repair mechanisms. This could be an explanation for the observed genotypic dependence of transformation rates in different plant species and plant genotypes. Gene copy number reconstructions revealed enhanced integration rates of plasmid sequences in transformed colonies derived from irradiated protoplasts. 相似文献
105.
T. Sakai J. Imamura 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1990,80(3):421-427
Summary Cytoplasts isolated from hypocotyl protoplasts of Raphanus sativus cv Kosena (cms line) by ultracentrifugation through Percoll/mannitol discontinuous gradient were fused with iodoacetamide(IOA)-treated protoplasts of Brassica napus cv Westar. Seventeen randomly selected regenerated plants were characterized for morphology and chromosome numbers. All of the regenerated plants had morphology identical to B. napus and 10 of them possessed the diploid chromosome number of B. napus. The remaining plants had chimeric or aneuploid chromosome numbers. The mitochondrial genomes in the 10 fusion products possessing the diploid chromosome numbers of B. napus were examined by Southern hybridization analysis. Four of the 10 plants contained mitochondrial DNA showing novel hybridization patterns. Of these 4 plants, 1 was male sterile, and 3 were male fertile. The remaining plants showed mitochondrial DNA patterns identical to B. napus and were male fertile. 相似文献
106.
Transfer of hygromycin resistance into Brassica napus using total DNA of a transgenic B. nigra line 总被引:3,自引:0,他引:3
The successful transfer of a marker gene (hpt gene) from Brassica nigra into B. napus via direct gene transfer was demonstrated. Total DNA was isolated from a hygromycin-resistant callus line, which contained three to five copies of the hpt gene. This line had been produced via direct gene transfer with the hygromycin resistance-conferring plasmid pGL2. The treatment of B. napus protoplasts with genomic DNA of B. nigra (HygR) resulted in relative transformation frequencies of 0.1–0.4%. Similar transformation rates were obtained in direct gene transfer experiments using B. napus protoplasts and plasmid pGL2. 相似文献
107.
László E. Heszky Zsolt Jekkel Abdel-Hamid Ali 《Plant Cell, Tissue and Organ Culture》1990,21(3):217-226
Reflexed saltmarsh-grass suspension cultures produced by seed callus were frozen to the liquid nitrogen temperature. Cooling rates, cryoprotectants and holding times were taken as a function of transfer temperatures. The highest survival of cells (45%) was found at a freezing rate of 1°C min-1, without cryoprotectant treatments. The cryoprotectants (proline, dimethyl sulphoxide, glycerol), used at different concentrations and transfer temperatures, increased the survival rate. The maximum value was 78% at 12.5% (w/v) of proline with –30°C transfer temperature. Considerable improvement of viability (from 0% to 95%) among the 12.5 and 15.0% (v/v) dimethyl sulphoxide cryopreserved cells was achieved by holding them at – 20°C for 10–30 min before plunging into the liquid nitrogen. A 20 min holding time at 15.0% (v/v) glycerol level and – 30°C transfer temperature significantly enhanced the viability of the explants from 42% to 92%. Plants were successfully regenerated from cells cryopreserved with proline (w/v) and dimethyl sulfoxide (v/v) levels of 12.5 and 15.0%, respectively. 相似文献
108.
The photosynthetic energy storage yield of uncoupled thylakoid membranes was monitored by photoacoustic spectroscopy at various measuring beam intensities. The energy storage rate as evaluated by the half-saturation measuring beam intensity (i50) was inhibited by 3-(3,4-dichlorophenyl)-1,1 dimethylurea, by heat inactivation or by artificial electron acceptors specific for photosystem I or photosystem II; and was activated by electron donors to photosystem I. The reactions involving both photosystems were all characterized by a similar maximal energy storage yield of 16±2 percent. The data could be interpreted if we assumed that the energy storage elicited by the photosystems at 35 Hz is detected at the level of the plastoquinone pool.Abbreviations PS
photosystem
- Tes
N-Tris [hydroxymethl] methyl-2-aminoethanesulfonic acid
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- DCIP
2,6-dichlorophenolindophenol
- FeCN
potassium ferricyanide
- DCBQ
2,5-dichlorobenzoquinone
- TMPD
N,N,N-tetramethyl-p-phenilenediamine 相似文献
109.
David P. Watts 《International journal of primatology》1990,11(1):21-45
Understanding the principles that underly primate social evolution depends on integrated analysis of data on behavioral ecology, demography, life history tactics, and social organization. In this paper, data on the behavioral ecology of gorillas are reviewed and comparisons made among the three subspecies. Gorillas are selective feeders; and, their patterns of food choice are consistent with models of feeding by large generalist herbivores. They rely heavily on terrestrial herbaceous vegetation, which provides an abundant supply of densely distributed food. Availability of this food varies little in space and time; and, gorilla foraging activity can maintain its productivity. The level of frugivory and the extent of seasonal variation in diet and habitat use vary among and within populations. Low variability in food distribution patterns makes cooperative defense of foraging areas not worthwhile; but, it also means that ecological costs associated with gregariousness are low. However, demographic and life history data on mountain gorillas show that these costs may be sufficient to reduce female reproductive success as group size increases. Advantages to being with high quality males apparently can outweigh these costs. The implications of these data for the evolution of the mountain gorilla social system, and the possible roles of male protection, predation, and female/female competition in this regard, are discussed. 相似文献
110.
ESR检测大鼠肺巨噬细胞释放的活性氧自由基 总被引:4,自引:0,他引:4
用ESR捕捉技术检测大鼠AM释放的活性氧自由基的性质表明:1.PMA和BCG均能刺激AM产生较强的OH·;能刺激人末稍血白细胞释放活性氧自由基的ConA和顺铂在本实验条件下未能使AM产生活性氧自由基信号。2.经膜活性剂PMA刺激的AM所释放活性氧自由基的高峰在刺激后2min,而经颗粒性物质BCG刺激,AM释放自由基的高峰时间明显后移。3.测试体系中的AM数过多或过少都不适合捕捉ESR信号。在本实验条件下,捕捉到最高自由基信号的AM终浓度为5×107AM/ml。4.测试体系中存在DETAPAC或EDTA,可使捕捉到的自由基信号明显增强。 相似文献