全文获取类型
收费全文 | 19509篇 |
免费 | 2862篇 |
国内免费 | 203篇 |
专业分类
22574篇 |
出版年
2023年 | 46篇 |
2022年 | 114篇 |
2021年 | 220篇 |
2020年 | 183篇 |
2019年 | 218篇 |
2018年 | 334篇 |
2017年 | 295篇 |
2016年 | 437篇 |
2015年 | 527篇 |
2014年 | 639篇 |
2013年 | 744篇 |
2012年 | 826篇 |
2011年 | 949篇 |
2010年 | 541篇 |
2009年 | 540篇 |
2008年 | 675篇 |
2007年 | 665篇 |
2006年 | 649篇 |
2005年 | 567篇 |
2004年 | 514篇 |
2003年 | 505篇 |
2002年 | 478篇 |
2001年 | 2293篇 |
2000年 | 2125篇 |
1999年 | 1488篇 |
1998年 | 430篇 |
1997年 | 453篇 |
1996年 | 380篇 |
1995年 | 353篇 |
1994年 | 264篇 |
1993年 | 224篇 |
1992年 | 721篇 |
1991年 | 591篇 |
1990年 | 501篇 |
1989年 | 393篇 |
1988年 | 309篇 |
1987年 | 241篇 |
1986年 | 179篇 |
1985年 | 141篇 |
1984年 | 88篇 |
1983年 | 65篇 |
1982年 | 44篇 |
1981年 | 41篇 |
1980年 | 26篇 |
1979年 | 31篇 |
1978年 | 27篇 |
1976年 | 31篇 |
1974年 | 24篇 |
1973年 | 30篇 |
1970年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
Qiu YC Zhou RH Kong XY Zhang SS Jia JZ 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2005,111(8):1524-1531
A powdery mildew resistance gene from Triticum urartu Tum. accession UR206 was successfully transferred into hexaploid wheat (Triticum aestivum L.) through crossing and backcrossing. The F1 plants, which had 28 chromosomes and an average of 5.32 bivalents and 17.36 univalents in meiotic pollen mother cells (PMC),
were obtained through embryos rescued owing to shriveling of endosperm in hybrid seed of cross Chinese Spring (CS) × UR206.
Hybrid seeds were produced through backcrossing F1 with common wheat parents. The derivative lines had normal chromosome numbers and powdery mildew resistance similar to the
donor UR206, indicating that the powdery mildew resistance gene originating from T. urartu accession UR206 was successfully transferred and expressed in a hexaploid wheat background. Genetic analysis indicated that
a single dominant gene controlled the powdery mildew resistance at the seedling stage. To map and tag the powdery mildew resistance
gene, 143 F2 individuals derived from a cross UR206 × UR203 were used to construct a linkage map. The resistant gene was mapped on the
chromosome 7AL based on the mapped microsatellite makers. The map spanned 52.1 cM and the order of these microsatellite loci
agreed well with the established microsatellite map of chromosome arm 7AL. The resistance gene was flanked by the microsatellite
loci Xwmc273 and Xpsp3003, with the genetic distances of 2.2 cM and 3.8 cM, respectively. On the basis of the origin and chromosomal location of the
gene, it was temporarily designated PmU. 相似文献
182.
Yang Z. T. Lu D. X. Hong E.-K. Zhang B. Y. Jiang M. C. Yang Y. J. Zhang D. J. 《Molecular Biology》2020,54(6):911-918
Molecular Biology - Brassica campestris L. is the important oil-bearing crop in China. Rapeseed cake is the main byproduct of rapeseed oil extraction. As the main active ingredient in rapeseed... 相似文献
183.
Direct detection of beta-1,3-glucanase isozymes on polyacrylamide electrophoresis and isoelectrofocusing gels 总被引:2,自引:0,他引:2
A procedure to assay isozymes of beta-1,3-glucanase directly on polyacrylamide gel electrophoresis (PAGE) and isoelectrofocusing (IEF) gels by using 2,3,5-triphenyltetrazolium chloride is described. The reagent reacts with reducing sugars released by beta-1,3-glucanases from the substrate laminarin. Acidic and neutral isozymes of beta-1,3-glucanase were detected and quantified on 17.5% native PAGE gels run with an anodic buffer system. A significant linear relationship (alpha = less than 0.01, R = 0.991) was observed between amounts of beta-1,3-glucanase loaded and intensity of bands stained with the reagent on native PAGE gels. A full isozyme pattern was obtained on 7.5% IEF gels with a pH range of 3.5-9.5. The IEF gels were heated in a microwave oven during the staining process to minimize diffusion. 相似文献
184.
Alexander F. Arendsen Jonathan Hadden Graeme Card Alan S. McAlpine Susan Bailey Vjacheslav Zaitsev Elizabeth H. M. Duke P. F. Lindley Monika Kröckel Alfred X. Trautwein Martinus C. Feiters John M. Charnock C. David Garner Sophie J. Marritt Andrew J. Thomson Ingeborg M. Kooter Michael K. Johnson Willy A. M. van den Berg Walter M. A. M. van Dongen W. R. Hagen 《Journal of biological inorganic chemistry》1998,3(1):81-95
The three-dimensional structure of the native "putative prismane" protein from Desulfovibrio vulgaris (Hildenborough) has been solved by X-ray crystallography to a resolution of 1.72?Å. The molecule does not contain a [6Fe-6S] prismane cluster, but rather two 4Fe clusters some 12?Å apart and situated close to the interfaces formed by the three domains of the protein. Cluster 1 is a conventional [4Fe-4S] cubane bound, however, near the N-terminus by an unusual, sequential arrangement of four cysteine residues (Cys 3, 6, 15, 21). Cluster 2 is a novel 4Fe structure with two μ2-sulfido bridges, two μ2-oxo bridges, and a partially occupied, unidentified μ2 bridge X. The protein ligands of cluster 2 are widely scattered through the second half of the sequence and include three cysteine residues (Cys 312, 434, 459), one persulfido-cysteine (Cys 406), two glutamates (Glu 268, 494), and one histidine (His 244). With this unusual mixture of bridging and external type of ligands, cluster 2 is named the "hybrid" cluster, and its asymmetric, open structure suggests that it could be the site of a catalytic activity. X-ray absorption spectroscopy at the Fe K-edge is readily interpretable in terms of the crystallographic model when allowance is made for volume contraction at 10?K; no Fe··Fe distances beyond 3.1?Å could be identified. EPR, Mössbauer and MCD spectroscopy have been used to define the oxidation states and the magnetism of the clusters in relation to the crystallographic structure. Reduced cluster 1 is a [4Fe-4S]1+ cubane with S?=?3/2; it is the first biological example of a "spin-admixed" iron-sulfur cluster. The hybrid cluster 2 has four oxidation states from (formally) all FeIII to three FeII plus one FeIII. The four iron ions are exchange coupled resulting in the system spins S?=?0, 9/2, 0 (and 4), 1/2, respectively, for the four redox states. Resonance Raman spectroscopy suggests that the bridging ligand X which could not be identified unambiguously in the crystal structure is a solvent-exchangeable oxygen. 相似文献
185.
186.
187.
Ionizing-radiation-induced damage in the DNA of cultured human cells. Identification of 8,5-cyclo-2-deoxyguanosine. 总被引:1,自引:0,他引:1 下载免费PDF全文
Epstein-Barr-virus-transformed peripheral-blood B-lymphocytes were gamma-irradiated at 0 degree C at doses from 10 to 100 Gy. The cells were immediately lysed and the DNA was isolated. Subsequently, the DNA was hydrolysed to 2'-deoxyribonucleosides with a mixture of DNAase I, venom and spleen exonucleases and alkaline phosphatase. The hydrolysate was dried, trimethylsilylated and analysed by capillary gas chromatography-mass spectrometry with selected-ion monitoring. The (5'R)- and (5'S)-diastereomers of 8,5'-cyclo-2'-deoxyguanosine were observed in a ratio of 1:3, and their formation was dose-dependent. It was possible to detect and characterize one such lesion in approx. 4 X 10(4) guanine nucleotide subunits of DNA. 相似文献
188.
Characterization of photosynthetic pathway of plant species growing in the eastern Tibetan plateau using stable carbon isotope composition 总被引:1,自引:0,他引:1
The photosynthetic pathway of plant species collected at Menyuan, Henan, and Maduo sites, east of Tibetan Plateau, China,
during the growing season were studied using stable carbon isotopes in leaves. The 232 samples leaves analyzed belonged to
161 species, 30 families, and 94 genera. The δ13C values (from −24.6 to − 29.2 ‰) indicated that all the considered species had a photosynthetic C3 pathway. The absence of plant species with C4 photosynthetic pathway might be due to the extremely low air temperature characterizing the Tibetan Plateau. The average
δ13C value was significantly (p<0.05) different between annuals and perennials at the three considered study sites. Hence the longer-lived species had greater
water-use efficiency (WUE) than shorter-lived species, that is, longer-lived species are better adapted to the extreme environmental
conditions of the Tibetan Plateau. 相似文献
189.
190.
A technique was developed for measuring the length of stylet insertion during adult whitefly probing. The distance that the labium shortens during a probe was shown to be equal to the length of stylets that were inserted into the plant tissue. The length of labial shortening then was measured in high-magnification video recordings of adult female silverleaf whitefly, Bemisia argentifolii, in conjunction with recording electrical penetration graphs (EPGs – AC method). Using a split-screen device, video images of the whitefly's labium during a probe and the EPG waveforms produced during the probe were recorded simultaneously on the same video tape. On playback, changes in labial length could be measured during specific EPG waveforms to determine the length of stylet insertion that occurred during the waveforms. The focus of the study was on two characteristics of the pathway phase sawtooth waveform: the frequency of voltage peaks and the increase in voltage level that occurs over time during sawtooth waveforms. The rate of stylet penetration was significantly and positively correlated with frequency of sawtooth waveform voltage peaks (r
2=0.33) and the length of stylet penetration was significantly and positively correlated (second-order polynomial) with the relative difference in voltage level between the beginning and end of the sawtooth waveform (r
2=0.43). Stylet advancement did not appear to occur during the few low-flat waveforms (unknown behavioral correlation) and high-flat waveforms (phloem phase) that were observed. Voltage drops occur sporadically during sawtooth waveforms, and these were associated with partial stylet withdrawal (indicated when the labium increased in length, but the probe was not terminated) with an accuracy of 99%. 相似文献