全文获取类型
收费全文 | 2371篇 |
免费 | 214篇 |
国内免费 | 240篇 |
专业分类
林业 | 153篇 |
农学 | 194篇 |
基础科学 | 193篇 |
795篇 | |
综合类 | 910篇 |
农作物 | 157篇 |
水产渔业 | 74篇 |
畜牧兽医 | 190篇 |
园艺 | 71篇 |
植物保护 | 88篇 |
出版年
2024年 | 13篇 |
2023年 | 90篇 |
2022年 | 165篇 |
2021年 | 163篇 |
2020年 | 132篇 |
2019年 | 134篇 |
2018年 | 79篇 |
2017年 | 98篇 |
2016年 | 110篇 |
2015年 | 81篇 |
2014年 | 112篇 |
2013年 | 234篇 |
2012年 | 159篇 |
2011年 | 175篇 |
2010年 | 91篇 |
2009年 | 123篇 |
2008年 | 97篇 |
2007年 | 92篇 |
2006年 | 92篇 |
2005年 | 60篇 |
2004年 | 49篇 |
2003年 | 60篇 |
2002年 | 35篇 |
2001年 | 37篇 |
2000年 | 34篇 |
1999年 | 38篇 |
1998年 | 32篇 |
1997年 | 26篇 |
1996年 | 25篇 |
1995年 | 27篇 |
1994年 | 28篇 |
1993年 | 24篇 |
1992年 | 24篇 |
1991年 | 17篇 |
1990年 | 13篇 |
1989年 | 21篇 |
1988年 | 12篇 |
1987年 | 15篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有2825条查询结果,搜索用时 15 毫秒
91.
《Communications in Soil Science and Plant Analysis》2012,43(5):383-388
Abstract Analytical data for Al and Fe extracted by different reagents is presented. It is concluded from the data that in podsolisation Al migrates mainly as inorganic gel while iron moves as organic chelated complexes. 相似文献
92.
《Communications in Soil Science and Plant Analysis》2012,43(4):331-339
Abstract A field experiment was conducted on an alkaline calcareous soil of Agronomy farm of the College of Agriculture, University of Udaipur to study the effect of sulphur on crop yield, leaf elemental composition, chlorophyll synthesis and activities of haematin enzymes. Application of elemental sulphur 21 days before planting with and without 0.1 per cent foliar sprays of H2SO4. increased crop yield by 137 to 197 per cent. Application of all these treatnents had no effect on nitrogen, phosphorus and potassium content of leaves but sulphur content was signficantly increased. Iron content of green leaves was decreased significantly 4 to 5 times together with an increase in the activity of catalase and peroxidase enzymes. Chlorosis in these soils appears to be on account of a reduced physiological availability of iron after absorption. 相似文献
93.
《Journal of plant nutrition》2013,36(10-11):2253-2265
Abstract T2 tobacco lines overexpressing soybean ferritin in the plastids (+TPs) or apoplasm (AFs) under the regulation of CaMV 35S promoter were grown on MS nutrient solution. After 1 month growth, statuses of six major divalent‐metals (Ca, Cu, Fe, Mg, Mn, and Zn) were measured in leaves and roots. Both +TPs and AFs showed enhanced growth (max. 1.7×) in leaves than the control line. The Fe contents in leaves of +TPs and AFs were significantly larger (1.9–2.8×) than that of the control line. The other metal contents in leaves of +TPs and AFs were almost the same as or less than those of the control line. In contrast to the result of leaves, the growth enhancement in roots was not clear in +TPs, but in AFs. Also, some of the non‐ferrous metal contents in roots of +TPs and AFs were dramatically increased compared with those of the control line (Mn, 1.9–10.4×; Zn, 1.6–2.3×), whereas the differences in content of Fe, Cu, Ca, and Mg were insignificant. These results demonstrated that the ferritin overexpression in apoplasm was as effective for inducing Fe accumulation as that in plastid. Under the normal metal‐balanced condition, even if the activation of Fe uptake related enzymes leads to the accumulation of non‐specific accumulation of divalent metal ions in roots, an Fe loading/unloading system and/or an internal translocator in xylem and phloem might specifically deliver Fe to the upper part of plants. 相似文献
94.
AIM:To investigate the role of reative oxygen species (ROS) generated by iron overload in activating the mitogen-activated protein kinase (MAPK) pathways and apoptosis. METHODS:Cultured human osteoblast cell line hFOB1.19 was treated with ferric ammonium citrate (FAC) at concentrations of 0~500 μmoL/L. The proliferation of hFOB1.19 cells was analyzed by MTT assay. Apoptosis was detected by flow cytometry with Annexin V/PI staining. The expression levels of p-ERK, p-JNK and p-p38 were determined by Western blotting 24 h after treatment with FAC. RESULTS:After treated with FAC, the cell proliferation was inhibited. The early apoptosis and total cell death were significantly increased. The levels of ROS were increased to (35.73±2.52)%, (62.89±4.24)% and (76.06±3.55)% with the increasing doses of FAC treatmen,respectively. The expression levels of p-ERK, p-JNK and p-p38 were also remarkably elevated in FAC groups. CONCLUSION:Iron overload increases intracellular ROS level, thus triggering the MAPK pathways and inducing apoptosis of human hFOB1.19 osteoblast cells. 相似文献
95.
Yoshikazu Kiriiwa Sunao Osumi Masanobu Endo Akira Nukaya Akio Morita Hiromi Yokota 《Soil Science and Plant Nutrition》2013,59(7):1119-1124
Abstract In alkaline soils, plant growth is impaired mainly by high pH and high concentration of bicarbonates. The bicarbonate concentration increases the pH value, and causes deficiency of iron. A bicarbonate-resistant cell line (BR line) of tobacco (Nicotiana tabacum L. cv. Burley21) was selected by adding excess bicarbonate ions (20 mmol L?1) to the culture medium. The pH of the medium was buffered 8.0 to 8.3. Under these conditions, about 80% of iron in the medium became insoluble. However, under such conditions, the BR line grew well. In this report, we examined some characteristics of the growth and iron uptake in the BR line under iron-deficient (i.e. high pH or no-iron) condition. At pH 5.8, the Fe3+ reduction activity was not significantly different between the non-selected line and the BR line. At pH 8.0, however, the Fe3+ reduction activity of the BR line was higher than that of the non-selected line. In no-iron condition, the growth of the non-selected line was markedly reduced after 2 weeks, while the BR line was not affected. The content of malic acid in both lines increased with the medium pH, and the content in the BR line was higher than that in the non-selected line. The BR line was able to adapt to the conditions, which restricted iron uptake, such as high bicarbonate concentration, high pH, and low iron conditions. The high ability of Fe3+ reduction was maintained at even high pH conditions. Further, the BR line may be able to improve the utilization of iron in the cells. 相似文献
96.
97.
98.
99.
SHEN Xueqing CUI Lijuan ZHOU Dongxing Resources Environmental Sciences College Northeast Agricultural University Harbin China 《东北农业大学学报(英文版)》2011,18(1):91-96
With the startup and execution of new socialistic countryside construction in Heilongjiang Province,the transition from castoff to resource is strengthened in the countryside,aiming at neat appearance of the countryside,clean production and saving energy.People produce biogas and provide the countryside with new energy by means of turning livestock's dejection into resources,composting of the plant and animal's leavings in the courtyard and even in the factory.It is helpful for the countryside to conserve t... 相似文献
100.
文章以某8V150柴油机为例,对其平衡轴进行了优化设计,使得双轴平衡机构不但能够100%的平衡二级往复惯性力,而且所设计的平衡轴尺寸小,质量轻,能够有效地消减机体的倾覆力矩,改善了发动机的振动特性,满足了设计要求. 相似文献