全文获取类型
收费全文 | 1868篇 |
免费 | 121篇 |
国内免费 | 24篇 |
专业分类
林业 | 64篇 |
农学 | 35篇 |
基础科学 | 31篇 |
175篇 | |
综合类 | 546篇 |
农作物 | 98篇 |
水产渔业 | 50篇 |
畜牧兽医 | 859篇 |
园艺 | 39篇 |
植物保护 | 116篇 |
出版年
2023年 | 13篇 |
2022年 | 13篇 |
2021年 | 22篇 |
2020年 | 34篇 |
2019年 | 27篇 |
2018年 | 31篇 |
2017年 | 35篇 |
2016年 | 39篇 |
2015年 | 28篇 |
2014年 | 41篇 |
2013年 | 116篇 |
2012年 | 81篇 |
2011年 | 97篇 |
2010年 | 65篇 |
2009年 | 44篇 |
2008年 | 66篇 |
2007年 | 79篇 |
2006年 | 76篇 |
2005年 | 67篇 |
2004年 | 66篇 |
2003年 | 51篇 |
2002年 | 51篇 |
2001年 | 30篇 |
2000年 | 37篇 |
1999年 | 41篇 |
1998年 | 21篇 |
1997年 | 13篇 |
1995年 | 20篇 |
1993年 | 13篇 |
1992年 | 25篇 |
1991年 | 33篇 |
1990年 | 28篇 |
1989年 | 27篇 |
1988年 | 29篇 |
1987年 | 24篇 |
1986年 | 17篇 |
1985年 | 29篇 |
1984年 | 30篇 |
1982年 | 16篇 |
1979年 | 14篇 |
1978年 | 22篇 |
1977年 | 17篇 |
1975年 | 19篇 |
1974年 | 19篇 |
1973年 | 12篇 |
1972年 | 13篇 |
1971年 | 15篇 |
1970年 | 14篇 |
1968年 | 15篇 |
1937年 | 11篇 |
排序方式: 共有2013条查询结果,搜索用时 15 毫秒
991.
992.
Light energy absorbed by the 576 bilin chromophores in the six rods of the phycobilisome of the cyanobacterium Synechocystis 6701 is funneled into a 1.5 x 10(6) dalton core. The 72 bilins of the core function as a single unit with respect to the rate-limiting processes for energy flow within these particles. 相似文献
993.
994.
Inhibition of GTPase activating protein stimulation of Ras-p21 GTPase by the Krev-1 gene product 总被引:33,自引:0,他引:33
M Frech J John V Pizon P Chardin A Tavitian R Clark F McCormick A Wittinghofer 《Science (New York, N.Y.)》1990,249(4965):169-171
Krev-1 is known to suppress transformation by ras. However, the mechanism of the suppression is unclear. The protein product of Krev-1, Rap1A-p21, is identical to Ras-p21 proteins in the region where interaction with guanosine triphosphatase (GTPase) activating protein (GAP) is believed to occur. Therefore, the ability of GAP to interact with Rap1A-p21 was tested. Rap1A-p21 was not activated by GAP but bound tightly to GAP and was an effective competitive inhibitor of GAP-mediated Ras-GTPase activity. Binding of GAP to Rap1A-p21 was strictly guanosine triphosphate (GTP)-dependent. The ability of Rap1A-p21 to bind tightly to GAP may account for Krev-1 suppression of transformation by ras. This may occur by preventing interaction of GAP with Ras-p21 or with other cellular proteins necessary for GAP-mediated Ras GTPase activity. 相似文献
995.
996.
Kling GW Clark MA Wagner GN Compton HR Humphrey AM Devine JD Evans WC Lockwood JP Tuttle ML Koenigsberg EJ 《Science (New York, N.Y.)》1987,236(4798):169-175
The sudden, catastrophic release of gas from Lake Nyos on 21 August 1986 caused the deaths of at least 1700 people in the northwest area of Cameroon, West Africa. Chemical, isotopic, geologic, and medical evidence support the hypotheses that (i) the bulk of gas released was carbon dioxide that had been stored in the lake's hypolimnion, (ii) the victims exposed to the gas cloud died of carbon dioxide asphyxiation, (iii) the carbon dioxide was derived from magmatic sources, and (iv) there was no significant, direct volcanic activity involved. The limnological nature of the gas release suggests that hazardous lakes may be identified and monitored and that the danger of future incidents can be reduced. 相似文献
997.
Aparicio S Chapman J Stupka E Putnam N Chia JM Dehal P Christoffels A Rash S Hoon S Smit A Gelpke MD Roach J Oh T Ho IY Wong M Detter C Verhoef F Predki P Tay A Lucas S Richardson P Smith SF Clark MS Edwards YJ Doggett N Zharkikh A Tavtigian SV Pruss D Barnstead M Evans C Baden H Powell J Glusman G Rowen L Hood L Tan YH Elgar G Hawkins T Venkatesh B Rokhsar D Brenner S 《Science (New York, N.Y.)》2002,297(5585):1301-1310
The compact genome of Fugu rubripes has been sequenced to over 95% coverage, and more than 80% of the assembly is in multigene-sized scaffolds. In this 365-megabase vertebrate genome, repetitive DNA accounts for less than one-sixth of the sequence, and gene loci occupy about one-third of the genome. As with the human genome, gene loci are not evenly distributed, but are clustered into sparse and dense regions. Some "giant" genes were observed that had average coding sequence sizes but were spread over genomic lengths significantly larger than those of their human orthologs. Although three-quarters of predicted human proteins have a strong match to Fugu, approximately a quarter of the human proteins had highly diverged from or had no pufferfish homologs, highlighting the extent of protein evolution in the 450 million years since teleosts and mammals diverged. Conserved linkages between Fugu and human genes indicate the preservation of chromosomal segments from the common vertebrate ancestor, but with considerable scrambling of gene order. 相似文献
998.
Rieder R Gellert R Anderson RC Brückner J Clark BC Dreibus G Economou T Klingelhöfer G Lugmair GW Ming DW Squyres SW d'Uston C Wänke H Yen A Zipfel J 《Science (New York, N.Y.)》2004,306(5702):1746-1749
The Alpha Particle X-ray Spectrometer on the Opportunity rover determined major and minor elements of soils and rocks in Meridiani Planum. Chemical compositions differentiate between basaltic rocks, evaporite-rich rocks, basaltic soils, and hematite-rich soils. Although soils are compositionally similar to those at previous landing sites, differences in iron and some minor element concentrations signify the addition of local components. Rocky outcrops are rich in sulfur and variably enriched in bromine relative to chlorine. The interaction with water in the past is indicated by the chemical features in rocks and soils at this site. 相似文献
999.
Squyres SW Arvidson RE Bell JF Brückner J Cabrol NA Calvin W Carr MH Christensen PR Clark BC Crumpler L Des Marais DJ D'Uston C Economou T Farmer J Farrand W Folkner W Golombek M Gorevan S Grant JA Greeley R Grotzinger J Haskin L Herkenhoff KE Hviid S Johnson J Klingelhöfer G Knoll A Landis G Lemmon M Li R Madsen MB Malin MC McLennan SM McSween HY Ming DW Moersch J Morris RV Parker T Rice JW Richter L Rieder R Sims M Smith M Smith P Soderblom LA Sullivan R Wänke H Wdowiak T Wolff M Yen A 《Science (New York, N.Y.)》2004,305(5685):794-799
The Mars Exploration Rover Spirit and its Athena science payload have been used to investigate a landing site in Gusev crater. Gusev is hypothesized to be the site of a former lake, but no clear evidence for lacustrine sedimentation has been found to date. Instead, the dominant lithology is basalt, and the dominant geologic processes are impact events and eolian transport. Many rocks exhibit coatings and other characteristics that may be evidence for minor aqueous alteration. Any lacustrine sediments that may exist at this location within Gusev apparently have been buried by lavas that have undergone subsequent impact disruption. 相似文献
1000.
Bulk Spin-Resonance Quantum Computation 总被引:6,自引:0,他引:6