全文获取类型
收费全文 | 48986篇 |
免费 | 2698篇 |
国内免费 | 33篇 |
专业分类
林业 | 1703篇 |
农学 | 1665篇 |
基础科学 | 251篇 |
5841篇 | |
综合类 | 8197篇 |
农作物 | 1545篇 |
水产渔业 | 2717篇 |
畜牧兽医 | 26339篇 |
园艺 | 574篇 |
植物保护 | 2885篇 |
出版年
2019年 | 419篇 |
2018年 | 779篇 |
2017年 | 823篇 |
2016年 | 743篇 |
2015年 | 607篇 |
2014年 | 750篇 |
2013年 | 1737篇 |
2012年 | 1348篇 |
2011年 | 1692篇 |
2010年 | 1154篇 |
2009年 | 1097篇 |
2008年 | 1685篇 |
2007年 | 1593篇 |
2006年 | 1499篇 |
2005年 | 1381篇 |
2004年 | 1394篇 |
2003年 | 1372篇 |
2002年 | 1184篇 |
2001年 | 1913篇 |
2000年 | 1984篇 |
1999年 | 1499篇 |
1998年 | 569篇 |
1997年 | 499篇 |
1996年 | 449篇 |
1995年 | 612篇 |
1994年 | 524篇 |
1993年 | 459篇 |
1992年 | 1152篇 |
1991年 | 1211篇 |
1990年 | 1178篇 |
1989年 | 1097篇 |
1988年 | 1056篇 |
1987年 | 1081篇 |
1986年 | 1035篇 |
1985年 | 966篇 |
1984年 | 803篇 |
1983年 | 684篇 |
1982年 | 421篇 |
1981年 | 383篇 |
1979年 | 635篇 |
1978年 | 500篇 |
1977年 | 441篇 |
1976年 | 408篇 |
1975年 | 451篇 |
1974年 | 523篇 |
1973年 | 507篇 |
1972年 | 531篇 |
1971年 | 449篇 |
1970年 | 424篇 |
1969年 | 465篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Impact of grassland contract policy on soil organic carbon losses from alpine grassland on the Qinghai–Tibetan Plateau 下载免费PDF全文
J. Cao Y. Gong E. T. Yeh N. M. Holden J. F. Adamowski R. C. Deo M. Liu J. Zhou J. Zhang W. Zhang S. Zhang D. Sheng S. Yang X. Xu M. Li Q. Feng 《Soil Use and Management》2017,33(4):663-671
Carbon storage in the soils on the Qinghai–Tibetan Plateau plays a very important role in the global carbon budget. In the 1990s, a policy of contracting collective grasslands to smaller units was implemented, resulting in a change from the traditional collective grassland management to two new management patterns: a multi‐household management pattern (MMP: grassland shared by several households without enclosures) and a single‐household management pattern (SMP: grassland enclosed and used by only one household). In 2016, 50 MMP and 54 SMP winter pastures on the Qinghai–Tibetan Plateau were sampled to assess the differences in soil organic carbon (SOC) between the two management patterns. Results showed that average SOC was significantly greater under MMP than under SMP, with an estimated 0.41 Mg C/ha/yr lost due to SMP following the new grassland contract. Based on the government's grassland policy, four grassland utilization scenarios were developed for both summer and winter pastures. We found that if the grassland were managed under SMP, likely C losses ranged between 0.31 × 107 and 6.15 × 107 Mg C/yr across the Qinghai–Tibetan Plateau relative to MMP, which more closely resembles pre‐1990s grassland management. Previous estimates of C losses have only considered land use change (with cover change) and ignored the impacts driven by land management pattern changes (without cover change). The new data suggest that C losses from the Qinghai–Tibetan Plateau are greater than previously estimated, and therefore that the grassland contract policy should be reviewed and SMP households should be encouraged to reunite into the MMP. These findings have potential implications for land management strategies not only on the Qinghai–Tibetan Plateau but also other grazing regions globally where such practices may exist. 相似文献
2.
In a feeding trial lasting for months Halothane-positive fattening pigs were put on a diet containing different concentrations of vitamin E and selenium. After a Myostress application vitamin E and selenium were additionally injected in order to examine stress resistance (CK-test) and regenerative capacity (histological examination of Musculus longissimus dorsi) of skeletal muscle. The study revealed that neither high dietary levels of vitamin E/selenium nor a vitamin E/selenium treatment applied after stress are capable of preventing stress related myopathy nor can they influence its healing up favourably. 相似文献
3.
4.
Abstract. A humoral antibody response was demonstrated by ELISA in rainbow trout immunized intraperitoneally with extracts from the branchiuran ectoparasite Argulus foliaceus. A similar immunization protocol produced a higher titre response in a rabbit. Both trout and rabbit identified several antigenic components on immunoblots. ELISA and immunoblotting indicated that rainbow trout and rabbit anti-A. foliaceus sera identified components from the parasitic copepods Lepeophtheirus salmonis and Caligus elongatus. 相似文献
5.
Glycoprotein I (gI) phenotypes and genotypes of 4 pseudorabies viral diagnostic isolates were evaluated by use of in vitro DNA amplification, monoclonal antibody binding, gI-specific serodiagnostic responses, and in vivo virulence approaches. Three viruses were avirulent and did not elicit gI-specific serologic responses, react with gI-specific monoclonal antibodies, or contain gI epitope-encoding DNA sequences. The fourth virus was virulent and did elicit a gI-specific serodiagnostic response. Compared with reference virulent pseudorabies viruses, however, the fourth isolate had reduced reactivity with a group of gI monoclonal antibodies and had a single nucleotide sequence substitution with a corresponding putative amino acid change in the epitopically dominant portion of the gI molecule. Presumably, the first 3 isolates represented diagnostic recoveries of viruses derived from gI-deleted modified-live pseudorabies viral vaccines, whereas the fourth isolate was a virulent but gI-aberrant wild-type virus. Thoroughly assessing the gI status of pseudorabies viral diagnostic isolates was considered to be essential in evaluating the epidemiologic importance of these viruses and in monitoring the validity of gI-based vaccine companion tests now used worldwide in pseudorabies control and eradication programs. 相似文献
6.
M Onuma Y Yasutomi M Yamamoto S Watarai T Yasuda Y Kawakami 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1989,36(2):139-147
Monoclonal antibody c143 against tumor-associated antigen (TAA) expressed on bovine leukemia cells was conjugated to liposomes containing adriamycin (ADM), and therapeutic effects of conjugates were examined in leukemic or preleukemic cows to prevent the progression of the disease. Five cows with TAA-positive in their peripheral blood lymphocytes were divided into two groups. Each group of cows received 4 injections of ADM alone (0.4 mg/kg) or c143-conjugated liposomes containing the same dose of ADM (L-AMD-c143) through the jugular vein at about 4 day intervals. In three animals treated with L-ADM-c143, the TAA-positive cells gradually decreased with treatment and finally two animals became TAA-negative during a 6 week period and a 14 week period after treatment, respectively. In the control, two animals treated with ADM alone showed only a slight decrease of TAA-positive cells. 相似文献
7.
E Oohashi K Yagi Y Uzuka S Tanabe T Sarashina T Ishida 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2001,63(11):1241-1243
The purpose of this study was to evaluate seasonal influences on thyroid hormone levels of healthy outdoor dogs in Hokkaido. We surveyed serum basal total thyroxine (tT4), free thyroxine (fT4), and canine thyroid-stimulating hormone (cTSH) levels, and tT4 levels after administration of TSH for a year. Basal tT4 levels decreased in January, and increased in August and September. fT4 levels increased in January and November. No significant seasonal variation was found in cTSH. tT4 levels after administration of TSH in August and November increased. These results suggested that the thyroid gland may have been activated in November. We should take seasonal variation into consideration when thyroid function is tested. 相似文献
8.
T. Sivakumar Virendranath & G. C. Srivastava 《Journal of Agronomy and Crop Science》2001,186(1):43-46
Grain yield and yield components (grains per ear, grain weight, 1000-grain weight, ear weight, ear seed ratio and dry matter partitioning between ear and seed) were examined in a wheat genotype (PBW-343) with well-filled grains and a Triticale genotype (DT-46) with poorly filled grains (showing grain shrivelling) grown in pots. Six days after anthesis (DAA), benzyladenine (BA) @2 µg ear−1 and abscisic acid (ABA) @4 µg ear−1 were injected at the base of the mother shoot ear in both species. It was observed that, in both wheat and Triticale , BA increased the grain weight, grain number and partitioning of dry matter between ear and seed, whereas ABA decreased the grain weight, grain number and dry matter partitioning between ear and seed. However, these decreases were slower in Triticale than in wheat. BA treatment increased the grain dry matter accumulation, which in turn resulted in better filling of grains and increased the grain weight in both wheat and Triticale . The average grain weight of Triticale was lower than that of wheat. Thus, it appears that variation in grain weight between wheat and Triticale might be due to different availabilities of growth-promoting phytohormones such as cytokinins and assimilates. 相似文献
9.
H Inokuma G Nane T Uechi Y Yonahara P Brouqui M Okuda T Onishi 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2001,63(11):1225-1227
Twelve (54.5%) of 22 free-roaming dogs in Ishigaki Island had tick infestation identified as Rhipicephalus sanguineus. There were 121 ticks recovered and consisted of 28 females, 58 males, 22 nymphs and 3 larvae. Infection of dogs possibly with canine ehrlichial pathogens was examined by both indirect immunofluorescence assay and polymerase chain reaction (PCR). Two dogs of the 13 examined were sero-positive for the human granulocytic ehrlichia agent, and one of two dogs was PCR positive for Ehrlichia platys. This dog had platelet numbers slightly lower than normal value, however, no morulae were found within platelet on peripheral blood smear stained with Giemsa. 相似文献
10.
V Rupasinghe K Iwatsuki-Horimoto S Sugii T Horimoto 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2001,63(6):609-618
A major capsid protein (MCP) gene homologue of porcine cytomegalovirus (PCMV) was identified. Sequence analysis indicated that the PCMV MCP gene is 4,026 nucleotides in length encoding a protein of 1,341 amino acid residues. The predicted molecular weight of the PCMV MCP is 151,456 Da, equivalent to those of other herpesvirus MCP counterparts. Phylogenetic analysis using herpesviral MCP gene sequences confirmed that PCMV is a betaherpesvirus with higher homology with human herpesvirus-6 and -7 than human and mouse cytomegaloviruses. The serum of pig experimentally infected with PCMV did not react with bacterially expressed MCP, suggesting that the PCMV MCP may not be related to the humoral immune response in the course of PCMV infection. Also, we established polymerase chain reaction (PCR) protocols using primers corresponding to MCP gene sequences for detection of PCMV infection. The PCR protocol would be effective for the diagnosis of slow-growing PCMV infection, for which traditional methods involving virus-isolation are not useful. 相似文献