全文获取类型
收费全文 | 521篇 |
免费 | 20篇 |
专业分类
林业 | 31篇 |
农学 | 12篇 |
132篇 | |
综合类 | 88篇 |
农作物 | 39篇 |
水产渔业 | 22篇 |
畜牧兽医 | 148篇 |
园艺 | 23篇 |
植物保护 | 46篇 |
出版年
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2018年 | 8篇 |
2017年 | 13篇 |
2016年 | 9篇 |
2015年 | 6篇 |
2014年 | 10篇 |
2013年 | 7篇 |
2012年 | 30篇 |
2011年 | 30篇 |
2010年 | 13篇 |
2009年 | 11篇 |
2008年 | 32篇 |
2007年 | 31篇 |
2006年 | 30篇 |
2005年 | 32篇 |
2004年 | 37篇 |
2003年 | 35篇 |
2002年 | 21篇 |
2001年 | 11篇 |
2000年 | 12篇 |
1999年 | 11篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1984年 | 5篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 6篇 |
1968年 | 2篇 |
1955年 | 2篇 |
1937年 | 4篇 |
1936年 | 5篇 |
1935年 | 9篇 |
1934年 | 3篇 |
排序方式: 共有541条查询结果,搜索用时 46 毫秒
111.
112.
Dieter Knösel 《Journal of pest science》1974,47(12):177-178
Zusammenfassung Im Mai 1970 traten im Bereich eines Textil-Veredlungswerkes auffällige Schädigungen an der Vegetation von Hausgärten auf. Das Schadbild entsprach einer Wuchsstoffeinwirkung; die Empfindlichkeit der Pflanzen war unterschiedlich. Anhand von Labor- und Gewächshaustesten konnte als Ursache die Immission eines Fä rbereihilfsmittels (Carrier) angenommen werden; es handelte sich dabei um einen substituierten Aromaten.
Summary Injuries to vegetation caused by a substance (Carrier) used for textile dyeing. In may 1970 an extraordinary case of injury to vegetation in the range of a textile dye-work occured. The symptoms were equal to those induced by auxins. A so called carrier substance, it concerned a substituted aromate, was indicated as causal agent.相似文献
113.
Ralph M. Nelson Jr. 《Wood Science and Technology》1992,26(5):335-342
Summary According to nonequilibrium thermodynamics, the local rate of entropy production is minimized for moist wood in the stationary state. Furthermore, the rate of entropy production due to moisture flow must be zero in this state. Conservation of energy applied to the steady flow of water vapor through an arbitrarily selected volume element of wood shows that the vapor entropy gradient is zero. Because the entropy production due to moisture flow must be balanced by a corresponding entropy flow away from the element, entropy gradients for bound water and water vapor are equal and the bound water entropy gradient also is zero. 相似文献
114.
- 1.
- Primary production on semiarid floodplains supports a diverse local and regional fauna. Reduced flooding from water resource development (WRD) may affect floodplain production by decreasing water and nutrient supply. 相似文献
115.
Silva LM Baums CG Rehm T Wisselink HJ Goethe R Valentin-Weigand P 《Veterinary microbiology》2006,115(1-3):117-127
Definition of virulent Streptococcus suis strains is controversial. One successful approach for identification of virulent European strains is differentiation of capsular serotypes (or the corresponding cps types) and subsequent detection of virulence-associated factors, namely the extracellular factor (EF, epf), the muramidase-released protein (MRP, mrp) and the hemolysin suilysin (SLY, sly). In this work we present a novel multiplex PCR (MP-PCR) and an mrp variant PCR for identification and characterization of virulent S. suis strains. These new methods were used to identify association of disease with particular profiles of virulence-associated genes. The MP-PCR allowed identification of S. suis through detection of the housekeeping gene gdh, differentiation of four cps types (1, 2, 7 and 9), and detection of epf, mrp, sly and arcA (arginine deiminase from S. suis). Furthermore, this study describes the first PCR assay for differentiation of at least six mrp variants. Expression of the corresponding size variants of MRP was shown for four of the six mrp variants, but was undetectable for the two larger mrp variants in the particular strains investigated. The results of this study suggest that cps7 strains are associated with pneumonia and that variation of mrp is very pronounced among these strains. Gene profiles of invasive, pneumonia and carrier S. suis isolates by combination of PCR assays allowed differentiation of 24 different genotypes among cps1, 2, 7 and 9 strains. Forty-five percent of the invasive S. suis diseases investigated in this study were caused by only two of these genotypes, namely cps2/mrp+/epf+/sly+ and cps9/mrp(*)/epf-/sly+. Thus, this study demonstrates for the first time a uniform profile of the particular virulence-associated genes for the vast majority of the investigated invasive cps9 strains. 相似文献
116.
Tuskan GA Difazio S Jansson S Bohlmann J Grigoriev I Hellsten U Putnam N Ralph S Rombauts S Salamov A Schein J Sterck L Aerts A Bhalerao RR Bhalerao RP Blaudez D Boerjan W Brun A Brunner A Busov V Campbell M Carlson J Chalot M Chapman J Chen GL Cooper D Coutinho PM Couturier J Covert S Cronk Q Cunningham R Davis J Degroeve S Déjardin A Depamphilis C Detter J Dirks B Dubchak I Duplessis S Ehlting J Ellis B Gendler K Goodstein D Gribskov M Grimwood J Groover A Gunter L Hamberger B Heinze B 《Science (New York, N.Y.)》2006,313(5793):1596-1604
We report the draft genome of the black cottonwood tree, Populus trichocarpa. Integration of shotgun sequence assembly with genetic mapping enabled chromosome-scale reconstruction of the genome. More than 45,000 putative protein-coding genes were identified. Analysis of the assembled genome revealed a whole-genome duplication event; about 8000 pairs of duplicated genes from that event survived in the Populus genome. A second, older duplication event is indistinguishably coincident with the divergence of the Populus and Arabidopsis lineages. Nucleotide substitution, tandem gene duplication, and gross chromosomal rearrangement appear to proceed substantially more slowly in Populus than in Arabidopsis. Populus has more protein-coding genes than Arabidopsis, ranging on average from 1.4 to 1.6 putative Populus homologs for each Arabidopsis gene. However, the relative frequency of protein domains in the two genomes is similar. Overrepresented exceptions in Populus include genes associated with lignocellulosic wall biosynthesis, meristem development, disease resistance, and metabolite transport. 相似文献
117.
Waite JH Combi MR Ip WH Cravens TE McNutt RL Kasprzak W Yelle R Luhmann J Niemann H Gell D Magee B Fletcher G Lunine J Tseng WL 《Science (New York, N.Y.)》2006,311(5766):1419-1422
The Cassini spacecraft passed within 168.2 kilometers of the surface above the southern hemisphere at 19:55:22 universal time coordinated on 14 July 2005 during its closest approach to Enceladus. Before and after this time, a substantial atmospheric plume and coma were observed, detectable in the Ion and Neutral Mass Spectrometer (INMS) data set out to a distance of over 4000 kilometers from Enceladus. INMS data indicate that the atmospheric plume and coma are dominated by water, with significant amounts of carbon dioxide, an unidentified species with a mass-to-charge ratio of 28 daltons (either carbon monoxide or molecular nitrogen), and methane. Trace quantities (<1%) of acetylene and propane also appear to be present. Ammonia is present at a level that does not exceed 0.5%. The radial and angular distributions of the gas density near the closest approach, as well as other independent evidence, suggest a significant contribution to the plume from a source centered near the south polar cap, as distinct from a separately measured more uniform and possibly global source observed on the outbound leg of the flyby. 相似文献
118.
Berton O McClung CA Dileone RJ Krishnan V Renthal W Russo SJ Graham D Tsankova NM Bolanos CA Rios M Monteggia LM Self DW Nestler EJ 《Science (New York, N.Y.)》2006,311(5762):864-868
Mice experiencing repeated aggression develop a long-lasting aversion to social contact, which can be normalized by chronic, but not acute, administration of antidepressant. Using viral-mediated, mesolimbic dopamine pathway-specific knockdown of brain-derived neurotrophic factor (BDNF), we showed that BDNF is required for the development of this experience-dependent social aversion. Gene profiling in the nucleus accumbens indicates that local knockdown of BDNF obliterates most of the effects of repeated aggression on gene expression within this circuit, with similar effects being produced by chronic treatment with antidepressant. These results establish an essential role for BDNF in mediating long-term neural and behavioral plasticity in response to aversive social experiences. 相似文献
119.
OBJECTIVES: To compare suture patterns (simple interrupted, modified pulley, horizontal mattress, double butterfly) by use of a novel in vitro model that quantifies force required for closure against tension. STUDY DESIGN: In vitro study. SAMPLE POPULATION: Suture constructs. METHODS: An in vitro suturing frame was constructed with extension springs to provide a standard resistance against movement of 2 panels of loops toward each other. Four different suture patterns were applied to the frame in randomized trials. The frame was affixed to a tensiometer that measured the force required for each suture pattern to close a fixed distance (3.81 cm) at a constant rate (5.08 cm/min) against the tension (0.6 kg/cm) of the extension springs. The closure distance and tension were selected subjectively to mimic tension encountered clinically during wound reconstruction oncologic surgical procedures. RESULTS: The modified pulley suture required the least force to close, followed by the double butterfly, simple interrupted, and horizontal mattress patterns. CONCLUSIONS: The modified pulley suture and double butterfly suture patterns require less force to close a given distance under tension than either simple interrupted or horizontal mattress suture patterns. CLINICAL RELEVANCE: Application of tension relieving suture techniques for fascia, subcutaneous, and buried-knot subdermal suturing should be considered to facilitate direct closure of wounds under tension. Modified pulley and double butterfly suture patterns offer some mechanical advantage by requiring less force to achieve closure compared with other suture patterns that might be used in reconstructive surgery. 相似文献
120.
Spin currents can apply useful torques in spintronic devices. The spin Hall effect has been proposed as a source of spin current, but its modest strength has limited its usefulness. We report a giant spin Hall effect (SHE) in β-tantalum that generates spin currents intense enough to induce efficient spin-torque switching of ferromagnets at room temperature. We quantify this SHE by three independent methods and demonstrate spin-torque switching of both out-of-plane and in-plane magnetized layers. We furthermore implement a three-terminal device that uses current passing through a tantalum-ferromagnet bilayer to switch a nanomagnet, with a magnetic tunnel junction for read-out. This simple, reliable, and efficient design may eliminate the main obstacles to the development of magnetic memory and nonvolatile spin logic technologies. 相似文献