全文获取类型
收费全文 | 461篇 |
免费 | 20篇 |
专业分类
林业 | 34篇 |
农学 | 21篇 |
基础科学 | 3篇 |
124篇 | |
综合类 | 70篇 |
农作物 | 6篇 |
水产渔业 | 19篇 |
畜牧兽医 | 178篇 |
园艺 | 5篇 |
植物保护 | 21篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 11篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 14篇 |
2015年 | 13篇 |
2014年 | 12篇 |
2013年 | 10篇 |
2012年 | 35篇 |
2011年 | 32篇 |
2010年 | 15篇 |
2009年 | 18篇 |
2008年 | 24篇 |
2007年 | 28篇 |
2006年 | 33篇 |
2005年 | 30篇 |
2004年 | 22篇 |
2003年 | 23篇 |
2002年 | 17篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1986年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1976年 | 4篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 7篇 |
1971年 | 12篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1967年 | 1篇 |
1963年 | 1篇 |
1940年 | 1篇 |
1938年 | 1篇 |
排序方式: 共有481条查询结果,搜索用时 46 毫秒
31.
32.
Valle L Serena-Acedo T Liyanarachchi S Hampel H Comeras I Li Z Zeng Q Zhang HT Pennison MJ Sadim M Pasche B Tanner SM de la Chapelle A 《Science (New York, N.Y.)》2008,321(5894):1361-1365
Much of the genetic predisposition to colorectal cancer (CRC) in humans is unexplained. Studying a Caucasian-dominated population in the United States, we showed that germline allele-specific expression (ASE) of the gene encoding transforming growth factor-beta (TGF-beta) type I receptor, TGFBR1, is a quantitative trait that occurs in 10 to 20% of CRC patients and 1 to 3% of controls. ASE results in reduced expression of the gene, is dominantly inherited, segregates in families, and occurs in sporadic CRC cases. Although subtle, the reduction in constitutive TGFBR1 expression alters SMAD-mediated TGF-beta signaling. Two major TGFBR1 haplotypes are predominant among ASE cases, which suggests ancestral mutations, but causative germline changes have not been identified. Conservative estimates suggest that ASE confers a substantially increased risk of CRC (odds ratio, 8.7; 95% confidence interval, 2.6 to 29.1), but these estimates require confirmation and will probably show ethnic differences. 相似文献
33.
CX3CR1-mediated dendritic cell access to the intestinal lumen and bacterial clearance 总被引:3,自引:0,他引:3
Niess JH Brand S Gu X Landsman L Jung S McCormick BA Vyas JM Boes M Ploegh HL Fox JG Littman DR Reinecker HC 《Science (New York, N.Y.)》2005,307(5707):254-258
Dendritic cells (DCs) and macrophages are critical to innate and adaptive immunity to the intestinal bacterial microbiota. Here, we identify a myeloid-derived mucosal DC in mice, which populates the entire lamina propria of the small intestine. Lamina propria DCs were found to depend on the chemokine receptor CX3CR1 to form transepithelial dendrites, which enable the cells to directly sample luminal antigens. CX3CR1 was also found to control the clearance of entero-invasive pathogens by DCs. Thus, CX3CR1-dependent processes, which control host interactions of specialized DCs with commensal and pathogenic bacteria, may regulate immunological tolerance and inflammation. 相似文献
34.
Manzke T Guenther U Ponimaskin EG Haller M Dutschmann M Schwarzacher S Richter DW 《Science (New York, N.Y.)》2003,301(5630):226-229
Opiates are widely used analgesics in anesthesiology, but they have serious adverse effects such as depression of breathing. This is caused by direct inhibition of rhythm-generating respiratory neurons in the Pre-Boetzinger complex (PBC) of the brainstem. We report that serotonin 4(a) [5-HT4(a)] receptors are strongly expressed in respiratory PBC neurons and that their selective activation protects spontaneous respiratory activity. Treatment of rats with a 5-HT4 receptor-specific agonist overcame fentanyl-induced respiratory depression and reestablished stable respiratory rhythm without loss of fentanyl's analgesic effect. These findings imply the prospect of a fine-tuned recovery from opioid-induced respiratory depression, through adjustment of intracellular adenosine 3',5'-monophosphate levels through the convergent signaling pathways in neurons. 相似文献
35.
Rendulic S Jagtap P Rosinus A Eppinger M Baar C Lanz C Keller H Lambert C Evans KJ Goesmann A Meyer F Sockett RE Schuster SC 《Science (New York, N.Y.)》2004,303(5658):689-692
Predatory bacteria remain molecularly enigmatic, despite their presence in many microbial communities. Here we report the complete genome of Bdellovibrio bacteriovorus HD100, a predatory Gram-negative bacterium that invades and consumes other Gram-negative bacteria. Its surprisingly large genome shows no evidence of recent gene transfer from its prey. A plethora of paralogous gene families coding for enzymes, such as hydrolases and transporters, are used throughout the life cycle of B. bacteriovorus for prey entry, prey killing, and the uptake of complex molecules. 相似文献
36.
Schiestl FP Peakall R Mant JG Ibarra F Schulz C Franke S Francke W 《Science (New York, N.Y.)》2003,302(5644):437-438
The "sexually deceptive" orchid Chiloglottis trapeziformis attracts males of its pollinator species, the thynnine wasp Neozeleboria cryptoides, by emitting a unique volatile compound, 2-ethyl-5-propylcyclohexan-1,3-dione, which is also produced by female wasps as a male-attracting sex pheromone. 相似文献
37.
Körner C Asshoff R Bignucolo O Hättenschwiler S Keel SG Peláez-Riedl S Pepin S Siegwolf RT Zotz G 《Science (New York, N.Y.)》2005,309(5739):1360-1362
Whether rising atmospheric carbon dioxide (CO2) concentrations will cause forests to grow faster and store more carbon is an open question. Using free air CO2 release in combination with a canopy crane, we found an immediate and sustained enhancement of carbon flux through 35-meter-tall temperate forest trees when exposed to elevated CO2. However, there was no overall stimulation in stem growth and leaf litter production after 4 years. Photosynthetic capacity was not reduced, leaf chemistry changes were minor, and tree species differed in their responses. Although growing vigorously, these trees did not accrete more biomass carbon in stems in response to elevated CO2, thus challenging projections of growth responses derived from tests with smaller trees. 相似文献
38.
Krause O Rieke GH Birkmann SM Le Floc'h E Gordon KD Egami E Bieging J Hughes JP Young ET Hinz JL Quanz SP Hines DC 《Science (New York, N.Y.)》2005,308(5728):1604-1606
Two images of Cassiopeia A obtained at 24 micrometers with the Spitzer Space Telescope over a 1-year time interval show moving structures outside the shell of the supernova remnant to a distance of more than 20 arc minutes. Individual features exhibit apparent motions of 10 to 20 arc seconds per year, independently confirmed by near-infrared observations. The observed tangential velocities are at roughly the speed of light. It is likely that the moving structures are infrared echoes, in which interstellar dust is heated by the explosion and by flares from the compact object near the center of the remnant. 相似文献
39.
Recent and subfossil calcareous structures resembling cystose and subclathrate Paleozoic stromatoporoids have been discovered in a sea-linked, stratified, alkaline crater lake on Satonda Island, Indonesia. The structures are produced by mats of coccoid cyanobacteria growing along the lakeshore from the water surface down to the O(2)-H(2)S interface located at a depth of 22.8 meters. Calcification of the mats is controlled by seasonal changes in calcium carbonate supersaturation in the epilimnion. The internally complex structures are a product of two different calcification processes: (i) periodic in vivo calcification of the surficial cyanobacterial layers by low-Mg calcite, and (ii) early postmortem calcification of the cyanobacterial aggregates below the mat surface by microbially precipitated aragonite. The finding supports the idea that Paleozoic stromatoporoids represent fossilized cyanobacteria (stromatolites). It also implies that the stromatoporoid-generating epicontinental seas during the early Paleozoic may have been more alkaline and had a higher carbonate mineral supersaturation than modern seawater. 相似文献
40.