全文获取类型
收费全文 | 4027篇 |
免费 | 194篇 |
国内免费 | 3篇 |
专业分类
林业 | 345篇 |
农学 | 520篇 |
基础科学 | 94篇 |
1034篇 | |
综合类 | 116篇 |
农作物 | 318篇 |
水产渔业 | 120篇 |
畜牧兽医 | 1202篇 |
园艺 | 119篇 |
植物保护 | 356篇 |
出版年
2023年 | 31篇 |
2022年 | 50篇 |
2021年 | 67篇 |
2020年 | 100篇 |
2019年 | 102篇 |
2018年 | 167篇 |
2017年 | 184篇 |
2016年 | 142篇 |
2015年 | 104篇 |
2014年 | 128篇 |
2013年 | 337篇 |
2012年 | 189篇 |
2011年 | 222篇 |
2010年 | 163篇 |
2009年 | 140篇 |
2008年 | 149篇 |
2007年 | 180篇 |
2006年 | 166篇 |
2005年 | 141篇 |
2004年 | 103篇 |
2003年 | 112篇 |
2002年 | 96篇 |
2001年 | 67篇 |
2000年 | 64篇 |
1999年 | 64篇 |
1998年 | 44篇 |
1997年 | 39篇 |
1996年 | 36篇 |
1995年 | 37篇 |
1994年 | 31篇 |
1993年 | 33篇 |
1992年 | 37篇 |
1991年 | 39篇 |
1990年 | 32篇 |
1989年 | 41篇 |
1988年 | 49篇 |
1987年 | 35篇 |
1986年 | 31篇 |
1985年 | 28篇 |
1984年 | 32篇 |
1983年 | 29篇 |
1982年 | 28篇 |
1980年 | 36篇 |
1979年 | 37篇 |
1978年 | 21篇 |
1976年 | 21篇 |
1970年 | 38篇 |
1969年 | 25篇 |
1968年 | 24篇 |
1967年 | 20篇 |
排序方式: 共有4224条查询结果,搜索用时 78 毫秒
41.
Chandra M Singh BR Shankar H Agarwal M Agarwal RK Sharma G Babu N 《Preventive veterinary medicine》2007,80(1):1-8
We screened serum samples of 1024 goats slaughtered for chevon in Bareilly in Northern India for Salmonella antibodies with indirect ELISA, MAT-H (microagglutination test using flagellar antigens e, n, x and 1, 5) and MAT-O (microagglutination test using somatic antigens 4, 12 and 3, 10, 15). Salmonella antibodies were detected in 48, 8 and 40%, goats using Salmonella-cytotoxi-I ELISA, MAT 'H' and MAT 'O', respectively. After adjusting for test accuracy, the seroprevalence were highest for Salmonella-cytotoxi-I ELISA (46%) followed by agglutinins against 'O' 3, 10, 15 (15%) and negligible for other agglutinins. With all 5 tests, prevalence of Salmonella antibodies was significantly higher in females than in males. No significant difference was evident in prevalence of Salmonella antibodies to different antigens in different age groups of male goats except for e, n, x agglutinins that were significantly more prevalent in young adult (<6-18 months) males than in adult (>18 months of age) or young (< or =6 months of age) goats. On the other hand, in females, prevalence of Salmonella-cytotoxin-I antibodies and e, n, x agglutinins differed significantly among three age groups, being the most prevalent in adult goats. As expected, the results of different tests had little or no correlation because the different tests targeted antibodies to different antigens. 相似文献
42.
Thakur Shikha Verma Subhash Chander Sharma Prem Lal Chandel Rajeshwar Singh Sharma Priyanka Sharma Shubham Sharma Prajjwal 《Phytoparasitica》2023,51(2):189-198
Phytoparasitica - Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae) is one of the most promising, effective and a common endoparasitoid of different aphid species including cabbage aphid,... 相似文献
43.
44.
Pooja A. R. Yogesh Pandey Meeti Punetha Anju Kala Hari Abdul Samad Gyanendra Singh Vikrant Singh Chouhan 《Reproduction in domestic animals》2023,58(1):60-72
The aim of the present study was to evaluate the expression and localization of lymphangiogenic factors (VEGF-C and VEGF-D), their receptor (VEGFR3) and lymphatic endothelial marker (LYVE1) in buffalo placenta during early pregnancy [EP], and to investigate the functional role of lymphangiogenic growth factors in placental lymphangiogenesis. The mRNA and protein expression of VEGF-C, VEGF-D, their receptor VEGFR3 and LYVE1 showed significant expression in EP1 (29–42 days) and EP2 stages (51–82 days) both in caruncle (maternal part) and cotyledon (foetal part) of the buffalo placenta. Immunoreactivity of VEGF-C, VEGF-D and LYVE1 was observed around the endometrial gland, in lymphatics and trophoblast cells, whereas VEGFR3 mainly localized in lymphatics of the caruncle and cotyledons. Cultured trophoblast cells were treated with VEGF-C/VEGF-D (50, 100 and 150 ng/ml) and combined doses of VEGF-C and VEGF-D (150 ng/ml) each for different time durations (24, 48 and 72 h). The mRNA expression of LYVE1 and PCNA was significantly (p < .001) upregulated with VEGF-C and VEGF-D and combined treatment (@150 ng/ml), as well as significantly downregulating Caspase-3 at 48 and 72 h. Thus, the present study provides evidence that lymphangiogenic factors are expressed in buffalo placental compartments and they may play a significant role in the regulation of placental function in water buffaloes. 相似文献
45.
G. S. Chaturvedi P. K. Aggarwal A. K. Singh M. G. Joshi S. K. Sinha 《Irrigation Science》1981,2(4):225-235
Summary The effect of irrigation on tillering and tiller mortality in varieties of wheat (Triticum aestivum and T. durum), triticale and barley was studied under field conditions. Low temperature in the early stages of growth promoted production of tillers whereas increase in temperature during extension growth phase increased tiller mortality. More than 1000 tillers m–2 were produced with five irrigations but 40% or more died. With limited water availability tiller production was reduced but so was their mortality. Grain yield in wheat and triticale was positively correlated with productive tillers and negatively correlated with the maximum number of tillers produced in wheat and barley grown under limited irrigation conditions. Varieties with a capacity to produce fewer tillers were identified. Some of them proved more stable in yield. No correlation was found between tiller number and grain yield in the frequently irrigated treatment. 相似文献
46.
A kinematic-wave model is developed for simulating the movement of soil moisture in unsaturated soils with plants. The model involves three free boundaries. Analytical solutions are derived when the plant roots are assumed to extract moisture at a constant rate and the upstream boundary condition is independent of time. Numerical solutions are the only resort when the moisture extraction and the upstream boundary condition both depend on time. 相似文献
47.
Time-independent (or steady-state) cases of channel flow were treated and errors of the kinematic-wave and diffusion-wave approximations derived for finite flow at the upstream end. The diffusion-wave approximation was found to be in excellent agreement with the dynamic wave representation, with error magnitudes of 0.2% for values of KF
0
2
7.5, where K is the kinematic-wave number and f
0 is the Froude number. Even for small values of KF
0
2
(e.g., KF
0
2
=0.75), the errors were typically in the range of 1.3 to 3.7%. The approximate analytical diffusion-wave solution performed poorly with error magnitudes greater than 30% even for large values of KF
0
2
. The kinematic-wave approximation was also found to be in good agreement with the dynamic-wave representation with errors of about 1.2% for KF
0
2
=7.5 and varying from 15 to 44% for KF
0
2
=0.75. 相似文献
48.
Summary This paper, second in a series of three, develops a mathematical model, using the volume balance approach, to simulate vertical and horizontal recession of border irrigation. An equation is proposed for computing Manning's roughness factor N in both laminar and transitional flow regimes in recession phases. The model has four parameters which can be determined experimentally. Experimental data from ten vegetated as well as nonvegetated borders were used to verify the model. Average difference (AD) between calculated and observed vertical recession times was less than 4.4 min, and between calculated and observed horizontal recession times less than 4.6 min for the ten experimental data sets. Average relative error (ARE) in computed horizontal recession was less than 13% for these data sets. The model was found to be especially accurate for Reynold's number between 1,800 and 2,500. 相似文献
49.
50.
Crop tolerance to land submergence is an important criterion for designing a surface drainage system for agricultural lands. This paper collates the available data from various places in India related to the studies on the submergence tolerance of crops. The paper hypothesizes that a piecewise linear model could be used to describe crop response to land submergence. According to this hypothesis, there would be no yield decline for a few initial days of submergence. If submergence continues beyond this period then there would be linear decline in yield. The unknown parameters in the model are: optimum yield, threshold time and the slope which represents the per cent yield reduction per day of additional submergence beyond the threshold.Data in respect of wheat, pigeon peas, cowpeas, pearlmillet, maize and groundnuts indicate that the model describes the data well, although in many cases the threshold is 0.0. The yield reduction varies from 5.3 to 23.2% for each day of submergence beyond the threshold. It appears that to allow for more than 1–2 days of submergence will result in more than 10% reducation in yield of dryfoot crops. For the maize crop, the seedling stage is the most sensitive stage followed by the silking stage. The grain formation stage is the least sensitive, although even at this stage the threshold is 0.0 and yield reduction is 9.3% for each day of submergence beyond the threshold. The data for 9 test crops from Texas and Venezuela were well described by the model. It is concluded that the piecewise linear model is a useful tool for describing submergence tolerance of crops and for working out surface drainage requirements for a given level of yield reduction. Frequency analysis of the daily rainfall data from some selected locations indicates that there is every likelihood of submergence at most of the stations. It is suggested that there is an urgent need for developing wet farming techniques analogous to dry farming techniques. 相似文献