全文获取类型
收费全文 | 12339篇 |
免费 | 734篇 |
国内免费 | 1020篇 |
专业分类
林业 | 1098篇 |
农学 | 698篇 |
基础科学 | 494篇 |
1152篇 | |
综合类 | 6311篇 |
农作物 | 887篇 |
水产渔业 | 420篇 |
畜牧兽医 | 1662篇 |
园艺 | 902篇 |
植物保护 | 469篇 |
出版年
2024年 | 97篇 |
2023年 | 222篇 |
2022年 | 580篇 |
2021年 | 527篇 |
2020年 | 498篇 |
2019年 | 540篇 |
2018年 | 337篇 |
2017年 | 590篇 |
2016年 | 358篇 |
2015年 | 591篇 |
2014年 | 679篇 |
2013年 | 706篇 |
2012年 | 1118篇 |
2011年 | 1099篇 |
2010年 | 1017篇 |
2009年 | 899篇 |
2008年 | 909篇 |
2007年 | 871篇 |
2006年 | 686篇 |
2005年 | 536篇 |
2004年 | 367篇 |
2003年 | 201篇 |
2002年 | 205篇 |
2001年 | 185篇 |
2000年 | 155篇 |
1999年 | 55篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 10篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1981年 | 4篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1965年 | 1篇 |
1962年 | 2篇 |
1957年 | 1篇 |
1956年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
991.
992.
AIM:To investigate the effects of radix pseudostellariae on cardiac function and matrix metalloproteinases (MMPs) in rat chronic heart failure induced by coronary artery ligation. METHODS:Rat model of chronic heart failure was produced by ligating the coronary artery for 6 weeks. The cardiac functions were determined by observing the hemodynamics parameters. mRNA expressions of MMP-2 and MMP-9 in left ventricular tissue were detected by RT-PCR and activities of MMPs were assayed by zemography.RESULTS:Cardiac function was remarkable turbulence after coronary artery ligation 6 weeks, according to the results of the hemodynamics. The mRNA contents and activities of MMP-2 and MMP-9 in left ventricular tissue were significantly elevated. Radix pseudostellariae remarkable ameliorated the cardiac functions, inhibited the mRNA contents and activities of MMP-2 and MMP-9 in left ventricular tissue of rat with chronic heart failure after continued 5 weeks treated with decoction of radix pseudostellariae. CONCLUSION:The decoction of radix pseudostellariae ameliorates cardiac functions of rat with chronic heart failure. The mechanism maybe involves in the inhibition of the MMP-2 and MMP-9 mRNA expression and activities in cardiac ventricles. 相似文献
993.
994.
It is one of the main characters of malignant tumors that malignant tumor cells invade surrounding tissues and metastasize to distant tissues. Multiple factors are involved in this complicated dynamic process. Metastasis is the major factor influencing recurrence and prognosis. Therefore, it is important to explore the mechanism of invasion and metastasis for reducing recurrence rate and mortality of malignant tumors. Engulfment and cell mobility (ELMO) family is one kind of conserved protein in evolutional process. It includes 3 members, ELMO1, ELMO2 and ELMO3. The members of ELMO family play an important role in cell phagocytosis and cell migration, and they also have close correlation with malignant tumor cell invasion and metastasis. In this paper, we review the progress of the relationship between ELMO family and malignant tumor invasion and metastasis. 相似文献
995.
Based on the second method of Lyapunov stability theory, the stability of non-equilibrium state for multiphase system is analysed. The results show that the dV/dt is always less than zero ff the V-function, which is defined as the entropy generation of the system, is greater than zero for the non-equilibrium state in linear zone, and the system is absolutely stable. On the other hand, the stability of the system in non-linear zone is determined with the symbol of dV/dt. 相似文献
996.
花江峡谷不同植被类型下土壤水分时空分布特征 总被引:14,自引:0,他引:14
花江峡谷是一个严重石漠化的喀斯特峡谷,水分是花江峡谷植物生长发育的主要限制因子,故在花江峡谷区如何选择适当的植被类型是充分利用降水和防止水土流失的一个重要环节。通过研究花江峡谷区不同植被类型下土壤水分的时空分布特征,探讨适合该区生态修复的植被类型,为峡谷区生态建设与水土保持提供依据。研究结果表明:(1)在空间分布上,多年生的柚木对土壤深层水分的影响较大;花椒树(特别是长势好的花椒树木)对土壤水分的保持具有明显作用。(2)在时间分布上,各种植被类型下的土壤含水量均随降雨量的多少而升降,但进入12月份在降雨量最低的情况下,花椒的土壤含水量甚至出现升高的现象,反映了花椒特有的保持水土、涵养水源的作用。研究结果证明大面积种植花椒树有利于提高研究区的生态、经济效益。 相似文献
997.
998.
The commonly used indicators are often too slow to reflect the operating status in time.Confronted with lacking reliable early-warning indices in the single-phase anaerobic digestion for kitchen waste which is easy to decay,lab-scale experiments of start-up and continuous operation process of anaerobic digestion for kitchen waste were carried out in the single-phase anaerobic reactor which is self-designed under mesophilic conditions.Those values which reflect the capacity of acidity-basicity resistance,including the ratio of bicarbonate alkalinity to total alkalinity (BA/TA),absolute testing value of volatile fatty acid (VFA) and the ratio of total concentration for volatile fatty acid to bicarbonate alkalinity (VFA/BA),are determinated to be the early-warning indices for acidification and imbalance of single-phase anaerobic digestion for kitchen waste.It is considered that,when VFA/BA>0.8,BA/TA<0.4 and VFA>3000mg/L,buffering capacity of the system is very poor,and the system might be out of control.Therefore,an immediately steps must be taken.While,when BA/TA≥0.7~0.8 and VFA/BA<0.4,the alkalinity of system is relatively better and the process can be operated with higher organic volumetric loading,which can raise the biogas-producing efficiency and get economic benefit. 相似文献
999.
1000.
彭珂珊 《河南科技大学学报(农学版)》2002,22(1):1-4
根据中国在20世纪末粮食达到5 000亿kg奋斗目标、解决13亿人的吃饭问题、人民生活得到改善的实际情况,针对2000年粮食减亏7%-9%的严峻形势,着重分析了粮食发展中的基础环境、粮食政策、生产投入、农业市场、生态环境等方面面临的严峻问题,为系统地选择相应的发展对策提供思路。 相似文献