全文获取类型
收费全文 | 751篇 |
免费 | 46篇 |
国内免费 | 1篇 |
专业分类
林业 | 28篇 |
农学 | 11篇 |
基础科学 | 13篇 |
87篇 | |
综合类 | 118篇 |
农作物 | 21篇 |
水产渔业 | 30篇 |
畜牧兽医 | 456篇 |
园艺 | 9篇 |
植物保护 | 25篇 |
出版年
2023年 | 6篇 |
2021年 | 11篇 |
2020年 | 20篇 |
2019年 | 18篇 |
2018年 | 12篇 |
2017年 | 20篇 |
2016年 | 17篇 |
2015年 | 17篇 |
2014年 | 17篇 |
2013年 | 23篇 |
2012年 | 28篇 |
2011年 | 28篇 |
2010年 | 16篇 |
2009年 | 19篇 |
2008年 | 31篇 |
2007年 | 28篇 |
2006年 | 27篇 |
2005年 | 23篇 |
2004年 | 28篇 |
2003年 | 20篇 |
2002年 | 30篇 |
2001年 | 20篇 |
2000年 | 18篇 |
1999年 | 22篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1992年 | 10篇 |
1991年 | 14篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 12篇 |
1987年 | 14篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1974年 | 12篇 |
1973年 | 10篇 |
1972年 | 5篇 |
1970年 | 6篇 |
1966年 | 8篇 |
1941年 | 6篇 |
1940年 | 7篇 |
1927年 | 5篇 |
排序方式: 共有798条查询结果,搜索用时 15 毫秒
51.
William J. Aspden Alexandra Rao Katherine Rose Paul T. Scott Iain J. Clarke Timothy E. Trigg John Walsh Michael J. D'Occhio 《Domestic animal endocrinology》1997,14(6)
Anterior pituitary gland contents of LH and LHß- and α-subunit mRNAs, and circulating concentrations of LH and testosterone, were determined in bulls treated with the LH-releasing hormone (LHRH) agonist deslorelin. Brahman (Bos indicus) bulls (14-month-old) were allocated to two groups and received the following: Control (n = 5), no treatment; Deslorelin (n = 4), four deslorelin implants (approximately 200 μg total deslorelin/day) for 36 d. Plasma concentrations of LH were higher in bulls treated with deslorelin on Day 1, had returned to typical levels by Day 8, and did not differ for control bulls and bulls treated with deslorelin from Day 8 to Day 29. Pituitary content of LH on Day 36 was reduced (P < 0.001) in bulls treated with deslorelin (33 ± 4 ng/mg) compared with control bulls (553 ± 142 ng/mg). Relative pituitary content of LHß-subunit mRNA was also reduced on Day 36 in bulls treated with deslorelin (Control, 0.65 ± 0.10; Deslorelin, 0.22 ± 0.04; P = 0.003). However, α-subunit mRNA relative content did not differ (Control, 0.73 ± 0.15; Deslorelin, 1.06 ± 0.12; P > 0.05). Plasma concentrations of testosterone were increased over the period of the experiment in the bulls treated with deslorelin compared with control bulls. This is the first demonstration of reduced pituitary content of LHß-subunit mRNA and LH, and unaltered content of α-subunit mRNA, in bulls treated with LHRH agonist. This was associated with apparently typical plasma concentrations of LH and elevated plasma testosterone. The anterior pituitary in bulls treated with LHRH agonist, therefore, undergoes classical desensitization and downregulation, but plasma LH and testosterone are not suppressed. 相似文献
52.
For the present and the foreseeable future the following options appear to be either usable or worth further exploration: mausolea; disposal in mines of various sorts, and perhaps in ice; in situ melt; and further chemical separations. The options are interdependent. It is too early to assess disposal in space, and disposal in the oceans remains unsafe for lack of adequate knowledge. Table 3 is a summary of the main ideas for which we have worked out (sometimes uncertain) costs. For the short term, ultimate disposal in deep mines is the best-developed plan. However, the related concept of in situ melt has significant advantages and should be realistically appraised. Further chemical separation with subsequent recycling of the actinides in a LMFBR should be investigated and implemented, for it would be universally beneficial; on the other hand, additional removal of strontium and cesium does not seem attractive. Thus, for the near future we make the following recommendations: 1) Provide temporary storage facilities to ensure that the projected commercial high-level wastes do not become a public hazard. The AEC adopts this view, and has stated an intention to construct such facilities. But because of the capriciousness of man and nature, a workable ultimate disposal scheme must be developed soon. 2) Fund other ultimate disposal schemes at the same rate as the salt mine project-say $1 million a year or more-to sharpen the technological issues, so that a decision can be reached in the next few years. The schemes should include (i) in situ melt, and the variation with a central repository; (ii) burial in mines other than salt mines (including Antarctic rocks and permanent ice); (iii) further chemical separation of actinides and recycling actinides in a LMFBR. 3) Maintain liaison with the developing space shuttle technology to insure that no opportunity is lost. The AEC has a commitment to hold safety foremost in its waste management program, but budget considerations and management priorities have downgraded the program. Past funding levels and management emphasis have yet to produce, after a decade and a half, one operational long-term storage facility-a sign of both commendable caution and inadequate work. If nuclear power is to resolve our energy needs in the coming decades, its benefits should not be delayed for lack of a viable management program for high-level wastes. 相似文献
53.
A map of the interactome network of the metazoan C. elegans 总被引:1,自引:0,他引:1
Li S Armstrong CM Bertin N Ge H Milstein S Boxem M Vidalain PO Han JD Chesneau A Hao T Goldberg DS Li N Martinez M Rual JF Lamesch P Xu L Tewari M Wong SL Zhang LV Berriz GF Jacotot L Vaglio P Reboul J Hirozane-Kishikawa T Li Q Gabel HW Elewa A Baumgartner B Rose DJ Yu H Bosak S Sequerra R Fraser A Mango SE Saxton WM Strome S Van Den Heuvel S Piano F Vandenhaute J Sardet C Gerstein M Doucette-Stamm L Gunsalus KC Harper JW Cusick ME Roth FP Hill DE Vidal M 《Science (New York, N.Y.)》2004,303(5657):540-543
54.
Rose DJ 《Science (New York, N.Y.)》1971,172(3985):797-808
55.
A stable cell line expressing a complementary DNA clone encoding the vesicular stomatitis virus glycoprotein fused and formed polykaryons at pH 5.5. The formation of polykaryons was dependent on the presence of glycoprotein anchored at the cell surface and could be prevented by incubation of cells with a monoclonal antibody to the glycoprotein. Fusion occurred at a pH 0.5 unit lower than that observed for cells infected with vesicular stomatitis virus. 相似文献
56.
57.
Redesigning metabolic routes: manipulation of TOL plasmid pathway for catabolism of alkylbenzoates 总被引:22,自引:0,他引:22
Increasing quantities of man-made organic chemicals are released each year into the biosphere. Some of these compounds are both toxic and relatively resistant to physical, chemical, or biological degradation, and they thus constitute an environmental burden of considerable magnitude. Genetic manipulation of microbial catabolic pathways offers a powerful means by which to accelerate evolution of biodegradative routes through which such compounds might be eliminated from the environment. In the experiments described here, a catabolic pathway for alkylbenzoates specified by the TOL plasmid of Pseudomonas was restructured to produce a pathway capable of processing a new substrate, 4-ethylbenzoate. Analysis of critical steps in the TOL pathway that prevent metabolism of 4-ethylbenzoate revealed that this compound fails to induce synthesis of the catabolic enzymes and that one of its metabolic intermediates inactivates catechol 2,3-dioxygenase (C23O), the enzyme that cleaves the aromatic ring. Consequently, the pathway was sequentially modified by recruitment of genes from mutant bacteria selected for their production of either an altered pathway operon regulator that is activated by 4-ethylbenzoate or an altered C23O that is less sensitive to metabolite inactivation. The redesigned pathway was stably expressed and enabled host bacteria to degrade 4-ethylbenzoate in addition to the normal substrates of the TOL pathway. 相似文献
58.
Comparative Earth History and Late Permian Mass Extinction 总被引:6,自引:0,他引:6
The repeated association during the late Neoproterozoic Era of large carbon-isotopic excursions, continental glaciation, and stratigraphically anomalous carbonate precipitation provides a framework for interpreting the reprise of these conditions on the Late Permian Earth. A paleoceanographic model that was developed to explain these stratigraphically linked phenomena suggests that the overturn of anoxic deep oceans during the Late Permian introduced high concentrations of carbon dioxide into surficial environments. The predicted physiological and climatic consequences for marine and terrestrial organisms are in good accord with the observed timing and selectivity of Late Permian mass extinction. 相似文献
59.
On the first day after hatching, domestic chicks were trained for 20, 60, 120, or 240 minutes with an imprinting stimulus. On the second day, they were all retrained for 60 minutes. The greater the chicks' experience on the first day, the lower the rate of incorporation of tritiated uracil into macromolecules in the anterior part of the forebrain roof on the second day. Such effects were not found in other brain regions, nor in any brain region of chicks that received similar treatment on the first day but were not retrained on the second. 相似文献
60.
Protein-metal ion binding site: determination with proton magnetic resonance spectroscopy 总被引:1,自引:0,他引:1
P I Rose 《Science (New York, N.Y.)》1971,171(971):573-574
Proton magnetic resonance spectra of aqueous gelatin were analyzed with respect to composition and molecular interactions. Aqueous gelatin complexes cobaltous ions in the pD range of approximately 3.5 to 7.5. Glutamyl and aspartyl side chains are shown to be the sites of binding. 相似文献