全文获取类型
收费全文 | 1149篇 |
免费 | 95篇 |
国内免费 | 1篇 |
专业分类
林业 | 84篇 |
农学 | 42篇 |
基础科学 | 2篇 |
213篇 | |
综合类 | 121篇 |
农作物 | 48篇 |
水产渔业 | 104篇 |
畜牧兽医 | 533篇 |
园艺 | 26篇 |
植物保护 | 72篇 |
出版年
2023年 | 9篇 |
2022年 | 19篇 |
2021年 | 43篇 |
2020年 | 37篇 |
2019年 | 63篇 |
2018年 | 43篇 |
2017年 | 36篇 |
2016年 | 46篇 |
2015年 | 43篇 |
2014年 | 41篇 |
2013年 | 61篇 |
2012年 | 85篇 |
2011年 | 91篇 |
2010年 | 47篇 |
2009年 | 37篇 |
2008年 | 62篇 |
2007年 | 68篇 |
2006年 | 51篇 |
2005年 | 58篇 |
2004年 | 47篇 |
2003年 | 48篇 |
2002年 | 41篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 8篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 8篇 |
1989年 | 4篇 |
1988年 | 10篇 |
1987年 | 5篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1972年 | 6篇 |
1971年 | 4篇 |
1969年 | 3篇 |
1968年 | 3篇 |
1964年 | 3篇 |
1933年 | 2篇 |
1931年 | 2篇 |
排序方式: 共有1245条查询结果,搜索用时 15 毫秒
71.
Rensing SA Lang D Zimmer AD Terry A Salamov A Shapiro H Nishiyama T Perroud PF Lindquist EA Kamisugi Y Tanahashi T Sakakibara K Fujita T Oishi K Shin-I T Kuroki Y Toyoda A Suzuki Y Hashimoto S Yamaguchi K Sugano S Kohara Y Fujiyama A Anterola A Aoki S Ashton N Barbazuk WB Barker E Bennetzen JL Blankenship R Cho SH Dutcher SK Estelle M Fawcett JA Gundlach H Hanada K Heyl A Hicks KA Hughes J Lohr M Mayer K Melkozernov A Murata T Nelson DR Pils B Prigge M Reiss B Renner T Rombauts S Rushton PJ 《Science (New York, N.Y.)》2008,319(5859):64-69
We report the draft genome sequence of the model moss Physcomitrella patens and compare its features with those of flowering plants, from which it is separated by more than 400 million years, and unicellular aquatic algae. This comparison reveals genomic changes concomitant with the evolutionary movement to land, including a general increase in gene family complexity; loss of genes associated with aquatic environments (e.g., flagellar arms); acquisition of genes for tolerating terrestrial stresses (e.g., variation in temperature and water availability); and the development of the auxin and abscisic acid signaling pathways for coordinating multicellular growth and dehydration response. The Physcomitrella genome provides a resource for phylogenetic inferences about gene function and for experimental analysis of plant processes through this plant's unique facility for reverse genetics. 相似文献
72.
73.
Wengelnik K Vidal V Ancelin ML Cathiard AM Morgat JL Kocken CH Calas M Herrera S Thomas AW Vial HJ 《Science (New York, N.Y.)》2002,295(5558):1311-1314
During asexual development within erythrocytes, malaria parasites synthesize considerable amounts of membrane. This activity provides an attractive target for chemotherapy because it is absent from mature erythrocytes. We found that compounds that inhibit phosphatidylcholine biosynthesis de novo from choline were potent antimalarial drugs. The lead compound, G25, potently inhibited in vitro growth of the human malaria parasites Plasmodium falciparum and P. vivax and was 1000-fold less toxic to mammalian cell lines. A radioactive derivative specifically accumulated in infected erythrocytes to levels several hundredfold higher than in the surrounding medium, and very low dose G25 therapy completely cured monkeys infected with P. falciparum and P. cynomolgi. 相似文献
74.
Aguado E Richelme S Nuñez-Cruz S Miazek A Mura AM Richelme M Guo XJ Sainty D He HT Malissen B Malissen M 《Science (New York, N.Y.)》2002,296(5575):2036-2040
The transmembrane protein LAT (linker for activation of T cells) couples the T cell receptor (TCR) to downstream signaling effectors. Mice homozygous for a mutation of a single LAT tyrosine residue showed impeded T cell development. However, later they accumulated polyclonal helper T (TH) cells that chronically produced type 2 cytokines in large amounts. This exaggerated TH2 differentiation caused tissue eosinophilia and massive maturation of plasma cells secreting to immunoglobulins of the E and G1 isotypes. This paradoxical phenotype establishes an unanticipated inhibitory function for LAT that is critical for the differentiation and homeostasis of TH cells. 相似文献
75.
Klein RF Allard J Avnur Z Nikolcheva T Rotstein D Carlos AS Shea M Waters RV Belknap JK Peltz G Orwoll ES 《Science (New York, N.Y.)》2004,303(5655):229-232
The development of osteoporosis involves the interaction of multiple environmental and genetic factors. Through combined genetic and genomic approaches, we identified the lipoxygenase gene Alox15 as a negative regulator of peak bone mineral density in mice. Crossbreeding experiments with Alox15 knockout mice confirmed that 12/15-lipoxygenase plays a role in skeletal development. Pharmacologic inhibitors of this enzyme improved bone density and strength in two rodent models of osteoporosis. These results suggest that drugs targeting the 12/15-lipoxygenase pathway merit investigation as a therapy for osteoporosis. 相似文献
76.
RNA secondary structure repression of a muscle-specific exon in HeLa cell nuclear extracts 总被引:44,自引:0,他引:44
B Clouet d'Orval Y d'Aubenton Carafa P Sirand-Pugnet M Gallego E Brody J Marie 《Science (New York, N.Y.)》1991,252(5014):1823-1828
The chicken beta-tropomyosin pre-messenger RNA (pre-mRNA) is spliced in a tissue-specific manner to yield messenger RNA's (mRNA's) coding for different isoforms of this protein. Exons 6A and 6B are spliced in a mutually exclusive manner; exon 6B was included in skeletal muscle, whereas exon 6A was preferred in all other tissues. The distal portion of the intron upstream of exon 6B was shown to form stable double-stranded regions with part of the intron downstream of exon 6B and with sequences in exon 6B. This structure repressed splicing of exon 6B to exon 7 in a HeLa cell extract. Derepression of splicing occurred on disruption of this structure and repression followed when the structure was re-formed, even if the structure was formed between two different RNA molecules. Repression leads to inhibition of formation of spliceosomes. Disrupting either of the two double-stranded regions could lead to derepression, whereas re-forming the helices by suppressor mutations reestablished repression. These results support a simple model of tissue-specific splicing in this region of the pre-mRNA. 相似文献
77.
Gilbert MT Kivisild T Grønnow B Andersen PK Metspalu E Reidla M Tamm E Axelsson E Götherström A Campos PF Rasmussen M Metspalu M Higham TF Schwenninger JL Nathan R De Hoog CJ Koch A Møller LN Andreasen C Meldgaard M Villems R Bendixen C Willerslev E 《Science (New York, N.Y.)》2008,320(5884):1787-1789
The Paleo-Eskimo Saqqaq and Independence I cultures, documented from archaeological remains in Northern Canada and Greenland, represent the earliest human expansion into the New World's northern extremes. However, their origin and genetic relationship to later cultures are unknown. We sequenced a mitochondrial genome from a Paleo-Eskimo human by using 3400-to 4500-year-old frozen hair excavated from an early Greenlandic Saqqaq settlement. The sample is distinct from modern Native Americans and Neo-Eskimos, falling within haplogroup D2a1, a group previously observed among modern Aleuts and Siberian Sireniki Yuit. This result suggests that the earliest migrants into the New World's northern extremes derived from populations in the Bering Sea area and were not directly related to Native Americans or the later Neo-Eskimos that replaced them. 相似文献
78.
Pyle AM 《Science (New York, N.Y.)》2005,309(5740):1530-1531
The number of naturally occurring RNA enzymes has just been expanded by the discovery of a new branching ribozyme. But this ribozyme has unexpected relatives: group I introns. 相似文献
79.
Busch L 《Science (New York, N.Y.)》1991,252(5007):772-773
80.