全文获取类型
收费全文 | 30545篇 |
免费 | 1295篇 |
国内免费 | 8篇 |
专业分类
林业 | 1107篇 |
农学 | 895篇 |
基础科学 | 174篇 |
4603篇 | |
综合类 | 3996篇 |
农作物 | 1176篇 |
水产渔业 | 1181篇 |
畜牧兽医 | 16586篇 |
园艺 | 338篇 |
植物保护 | 1792篇 |
出版年
2021年 | 231篇 |
2020年 | 273篇 |
2019年 | 337篇 |
2018年 | 608篇 |
2017年 | 672篇 |
2016年 | 574篇 |
2015年 | 372篇 |
2014年 | 558篇 |
2013年 | 1679篇 |
2012年 | 868篇 |
2011年 | 1128篇 |
2010年 | 815篇 |
2009年 | 764篇 |
2008年 | 1092篇 |
2007年 | 1060篇 |
2006年 | 900篇 |
2005年 | 726篇 |
2004年 | 730篇 |
2003年 | 664篇 |
2002年 | 592篇 |
2001年 | 745篇 |
2000年 | 745篇 |
1999年 | 546篇 |
1998年 | 245篇 |
1997年 | 228篇 |
1995年 | 269篇 |
1992年 | 404篇 |
1991年 | 415篇 |
1990年 | 432篇 |
1989年 | 442篇 |
1988年 | 348篇 |
1987年 | 354篇 |
1986年 | 384篇 |
1985年 | 343篇 |
1984年 | 332篇 |
1983年 | 303篇 |
1979年 | 483篇 |
1978年 | 328篇 |
1977年 | 371篇 |
1976年 | 468篇 |
1975年 | 485篇 |
1974年 | 526篇 |
1973年 | 486篇 |
1972年 | 438篇 |
1971年 | 354篇 |
1970年 | 373篇 |
1969年 | 435篇 |
1968年 | 441篇 |
1967年 | 446篇 |
1966年 | 438篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Preparation and evaluation of antigens used in serological tests for caprine syncytial retrovirus antibody in sheep and goat sera 总被引:3,自引:0,他引:3
Methods used to prepare antigens from caprine syncytial retrovirus (CSR) for use in the agarose gel immunodiffusion test (AGID) or an indirect enzyme-linked immunosorbent assay (ELISA) are described. Caprine and ovine sera were tested for antibody to CSR using the AGID test and ELISA incorporating a caprine system (CSR antigen and rabbit anti-goat IgG) or an ovine system (maedi-visna virus antigen and rabbit anti-sheep IgG). Good correlation was achieved in the results of the 3 tests when sera were devoid of antibody or were strongly positive. Variations in the results on weakly positive sera were considered to be more a matter of interpretation than due to basic differences in the reagents employed. 相似文献
42.
Twelve anestrous adult Greyhound bitches were used to study a regimen for induction of estrus. Once daily, 7 bitches were given diethylstilbestrol (DES; 5 mg, PO) until sanguineous vaginal discharge and vulvar edema were observed (designated as day 1 of proestrus) and for 2 days thereafter. If no response was elicited after 7 days, a doubled DES dose was given for up to an additional 7 days. Luteinizing hormone (5 mg, IM) was given on day 5 of proestrus, and follicle-stimulating hormone (10 mg, IM) was given on days 9 and 11 of proestrus. Bitches were bred once on day 13. Five bitches were used as a control group; they were given candy tablets for 7 days (first day on tablets, treatment day 1) and 0.9% NaCl (1.0 ml, IM) on treatment days 12, 16, and 18. The 7 bitches treated with DES had a mean proestrus period of 7.7 days and a mean estrus period of 5.7 days up to the day of mating. After mating, they had a mean gestation interval of 64 days and delivered a mean of 4 pups/litter. In 5 bitches, initial treatment with 5 mg of DES/day induced proestrus within 7 days; however, in 2 bitches, additional treatment with 10 mg of DES/day was needed for 5 and 6 days, respectively. Serum estradiol-17 beta and progesterone concentrations remained at base line during the period of DES treatment. Concentrations of both hormones increased after injection with luteinizing hormone and remained high for the next 4 days.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
43.
44.
DM yield and N uptake data are presented from primary growth and two successive regrowths of perennial ryegrass treated with combinations of three N treatments for the primary growth viz. 0, 50 and 100 kg N/ha (PN) and four N treatments applied for the second growths, viz. 0, 33, 66 and 100 kg N/ha (SN). Primary growth gave a response of 24·2 kg DM/kg applied N to PN50 with only a further l±0 kg DM/kg applied N from the second PN increment. A significant interaction between PN and SN treatments was shown in second growth. The residual DM response to PN was highest at SN0 and reduced as the level of SN was raised. Substantially greater residual responses to PN treatments were shown in the third growth. Third growth DM responses to SN treatments were high. High apparent recovery of fertilizer N reached 111% of primary N where SN66 followed PN50. High available soil N is partly responsible for both high apparent recovery of N and high DM response. The latter appears to be associated with inclusion of growths given no fertilizer N so that the full residual effects of fertilizer N and ‘priming’ of available soil N can be realised. 相似文献
45.
Specific features of the development of redox systems in the soils of coal mine dumps in Kemerovo oblast were studied. The
quantitative characteristics of the fractional composition of the oxidized and reduced components in these soils were obtained,
and their heterogeneity was shown. Distribution patterns of the reduced and oxidized components in the parent material of
these specific technogenic landscapes in the course of soil evolution were revealed. 相似文献
46.
47.
Kellogg V 《Science (New York, N.Y.)》1923,58(1505):337-341
48.
Mishra N Vilcek S Rajukumar K Dubey R Tiwari A Galav V Pradhan HK 《Research in veterinary science》2008,84(3):507-510
Since cattle are widely infected by bovine viral diarrhea virus (BVDV) in India, we searched for pestivirus infection in yaks. Of 71 pure and crossbred yaks from Himalayan region, pestivirus antigen was detected by Ag-ELISA in three animals. Pestivirus in leukocyte and cell culture isolated virus samples originating from positive yaks was also confirmed by RT-PCR using panpestivirus specific primers selected from 5'-untranslated region (5' UTR). The 5' UTR, N(pro) and E2 regions were sequenced and used for genetic typing. Phylogenetic analysis revealed that pestiviruses detected in three Himalayan yaks were similar genetically, belonging to BVDV-1. Antigenic characterisation of yak pestivirus also confirmed the typing as BVDV-1. This is the first report on the identification of BVDV type 1 in yaks. 相似文献
49.
Pharmacokinetics of topically applied ciprofloxacin in tears of mesocephalic and brachycephalic dogs
OBJECTIVE: To evaluate the pharmacokinetics of ophthalmic ciprofloxacin in the tear film of normal mesocephalic and brachycephalic dogs. ANIMALS STUDIED: Twenty mesocephalic dogs and 15 brachycephalic dogs. PROCEDURES: Thirty-five microliters of ciprofloxacin were placed on the cornea of both eyes of each dog. Five brachycephalic dogs were used twice. A tear-test strip placed in the ventral cul de sac for 30 s was used to obtain samples. The tear film of each eye was sampled once at eight time-points post administration, resulting in five samples at each time-point. Samples were evaluated using high performance liquid chromatography. Data from the two skull types were compared using the unpaired two-tailed t-test. RESULTS: The mean concentration of ciprofloxacin in the tears of mesocephalic dogs was 192.8 +/- 269.97, 140.6 +/- 91.06, 56.60 +/- 28.47, 13.6 +/- 6.3, 43.25 +/- 59.71, 16.6 +/- 10.62, 15.6 +/- 13.16 and 6.25 +/- 9.84 microg/g at 5, 10, 15, 30 min and 1, 2, 4 and 6 h, respectively. The mean concentration of ciprofloxacin in the tears of brachycephalic dogs was 272.6 +/- 106.21, 144.4 +/- 142.32, 131.2 +/- 147.07, 75 +/- 80.07, 40.8 +/- 30.35, 35 +/- 21.98, 52.75 +/- 51.87 and 8.6 +/- 12.10 microg/g at 5, 10, 15, 30 min and 1, 2, 4 and 6 h, respectively. There was no statistical difference in tear concentration at any time-point between skull types. CONCLUSIONS: Topical application of ciprofloxacin resulted in a mean tear concentration of ciprofloxacin that remained above the MIC(90) levels for most pathogenic bacteria for 6 h in normal mesocephalic and brachycephalic dogs. 相似文献
50.