全文获取类型
收费全文 | 2124篇 |
免费 | 123篇 |
国内免费 | 62篇 |
专业分类
林业 | 240篇 |
农学 | 69篇 |
基础科学 | 23篇 |
380篇 | |
综合类 | 184篇 |
农作物 | 115篇 |
水产渔业 | 214篇 |
畜牧兽医 | 841篇 |
园艺 | 76篇 |
植物保护 | 167篇 |
出版年
2024年 | 4篇 |
2023年 | 24篇 |
2022年 | 34篇 |
2021年 | 64篇 |
2020年 | 48篇 |
2019年 | 44篇 |
2018年 | 93篇 |
2017年 | 85篇 |
2016年 | 81篇 |
2015年 | 47篇 |
2014年 | 77篇 |
2013年 | 151篇 |
2012年 | 119篇 |
2011年 | 131篇 |
2010年 | 102篇 |
2009年 | 92篇 |
2008年 | 102篇 |
2007年 | 106篇 |
2006年 | 77篇 |
2005年 | 99篇 |
2004年 | 56篇 |
2003年 | 95篇 |
2002年 | 98篇 |
2001年 | 95篇 |
2000年 | 64篇 |
1999年 | 47篇 |
1998年 | 21篇 |
1997年 | 13篇 |
1996年 | 15篇 |
1995年 | 29篇 |
1994年 | 14篇 |
1993年 | 9篇 |
1992年 | 16篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 19篇 |
1988年 | 15篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1972年 | 5篇 |
1967年 | 9篇 |
1966年 | 6篇 |
排序方式: 共有2309条查询结果,搜索用时 125 毫秒
41.
Laing KJ Pilström L Cunningham C Secombes CJ 《Veterinary immunology and immunopathology》1999,72(1-2):45-53
A partial nucleotide sequence of transforming growth factor-beta3 (TGF-beta3) has been isolated from the Siberian sturgeon (Acipenser baeri), rainbow trout (Oncorhynchus mykiss) and European eel (Anguilla anguilla), confirming a ubiquitous presence in the ray-finned (Actinopterygian) bony fish. The bony fish TGF-beta3 is highly conserved, with some 83-84% nucleotide identity (coding region) and 90-95% predicted amino acid identity to known homeotherm TGF-beta3's. Far lower homologies are apparent with other known TGF-beta isoforms in fish (e.g. 64-66% and 81-82% amino acid identity to trout TGF-beta 1/5 and carp TGF-beta2 respectively). Phylogenetic tree analysis showed that the fish TGF-beta3's clustered with the known homeotherm TGF-beta3's. The relatively tight clustering of TGF-beta1, TGF-beta2 and TGF-beta3 was in contrast to the TGF-beta5's, which are clearly a more heterogenous group. 相似文献
42.
The aim of this research was to observe the effects of cyclophosphamide and its uroprotective agents, mesna and hyperbaric oxygen (HBO), on the motility of urinary bladder muscle in guinea pigs. In the experimental groups, mesna and cyclophosphamide were intraperitoneally injected at a dose of 21.5 mg/kg and 68.1 mg/kg, respectively. For the combination of mesna and cyclophosphamide, one dose of mesna was injected 20 min before cyclophosphamide administration and three additional injections of mesna were repeated every three hours. A total of 8 HBO exposures were performed at 2.8 ATA for 90 min twice daily for another experimental group. In the HBO and cyclophosphamide combined group 5 HBO exposures were given prophylactically before cyclophosphamide. The combination of mesna, HBO and cyclophosphamide was administered by the same procedure. The contractions obtained in response to acetylcholine (ACh, 10(-4) M) in the control group were reduced using cyclophosphamide and HBO individually, but not by mesna. However, the contractions belonging to the various combinations of these three agents were not different from those seen in the control group. On the other hand, the combinations of cyclophosphamide, mesna and HBO showed higher responses to ACh than the groups in which cyclophosphamide and HBO were used individually, while the responses elicited by the cyclophosphamide and HBO combination were greater than those seen in the group treated with HBO only. 相似文献
43.
Abstract. Nitrate leaching in lysimeters containing a tropical sandy agricultural soil was studied over two summers with maize ( Zea mays L.) and one winter season with wheat ( Triticum aestivum L.). The treatments included two moisture regimes and two nitrogen sources, cattle manure and inorganic fertilizer-N (either ammonium nitrate or ammonium sulphate) applied at 100 kg N/ha in the summers. Neither manure nor fertilizer-N was applied in the intervening winter. Leachate volume from the manured lysimeters was mostly larger than from fertilized ones because of poor growth and less evapotranspiration. The largest seasonal nitrate loads (17–39 kg N/ha) were obtained in the wet summer immediately after installation of the lysimeters. Nitrate loads in winter (3.7–18.6 kg N/ha) were larger than those obtained in fertilized (0.6 and 9.3 kg N/ha) and manured (0.3 and 3.0 kg N/ha) lysimeters for the two moisture regimes in the second summer. The drier conditions in the second summer decreased N-mineralization and leaching of manure. 相似文献
44.
45.
A 4-year study of parasitoids attackingChrysoperla carnea (Stephens) in the cotton fields of Çukurova, Turkey, revealed the activities of three principal taxa:Telenomus sp. nr.suvae attacks the eggs ofC. carnea: Catolaccus sp. andBaryscapus sp. are larval and pupal parasitoids, respectively. In general, percent egg parasitism increased starting from the second half of June and into July, then decreased until the beginning of August before rising again at the end of growing season. During the early season, weekly parasitism was found to be as high as 94%. Overall, seasonal egg parasitism varied between 13.6% and 62.0% among all study sites. According to the results of a one-year field study at Hac?ali, total larval and pupal parasitism was found to be 12.5% and 55.6%, respectively. Therefore, different factors influencing the effectiveness of the generalist predatorC. carnea against cotton pests, and the differential effects of cotton treatments on both host and parasitoids, need to be evaluated. 相似文献
46.
The Aphidoidea (Homoptera) has 29 species which attack coniferous trees in Turkey. The family Aphididae has 25 (Aphidinae, 1; Lachninae, 22; Mindarinae, 2) species and the Adelgidae, 4. The tribe Cinarini in Lachninae has alone 22 species most of which are important. Especially Cinara cedri Mimeur on Cedrus libani and C. pilicornis (Hartig) on Picea spp. are harmful species. Schizolachnus pineti (Fabricius) is also very important. An Eastern Palearctic species in the tribe Macrosiphini in Aphidinae, Elatobium momii (Shinji), is numerous on Abies bornmülleriana in Bursa-Uluda forests. Pineus orientalis (Dreyfus) in the family of Adelgidae (Chermesidae) is the most destructive in our Picea orientalis forests in Artvin area (Eastern Black-Sea Section). 21 species out of 29 aphids on coniferous trees are of European origin; only 4 are Mediterranean, 2 Caucasus and Turkistan, one Eastern Palearctic and one of Cosmopolitan origin. 相似文献
47.
Effect of heat stress on oxidative stress, lipid peroxidation and some stress parameters in broilers 总被引:6,自引:0,他引:6
1. This study was conducted to determine the effects of heat stress on fearfulness, leucocyte components, oxidative stress and lipid peroxidation in two commercial broiler strains, Cobb (C) and Ross (R). 2. At 36 and 37 d of age birds were exposed to 38 +/- 1 degree C for 3 h. Rectal temperatures, duration of tonic immobility (TI), haematocrit values, proportions of leucocyte components (heterophil, lymphocyte, basophil, eosinophil, monocyte), malondialdehyde (MDA) concentrations and antioxidant enzyme activities (CAT, SOD, GPx) of all the birds were determined, before and after heat treatment. 3. Rectal temperatures increased and haematocrit values decreased in birds exposed to heat stress. Heat stress caused a significant increase in heterophil/lymphocyte and in basophil ratios. 4. Exposing birds to heat stress increased duration of TI, suggesting heat-stressed birds tended to be more fearful. 5. Heat stress resulted in a significant Genotype x Treatment interaction for MDA concentration. CAT, SOD and GPx activities; MDA concentrations in heat-stressed R strain birds were greater than in heat-stressed C strain birds. 相似文献
48.
49.
50.