全文获取类型
收费全文 | 71311篇 |
免费 | 4434篇 |
国内免费 | 6387篇 |
专业分类
林业 | 5045篇 |
农学 | 3835篇 |
基础科学 | 3248篇 |
7040篇 | |
综合类 | 35199篇 |
农作物 | 5208篇 |
水产渔业 | 2744篇 |
畜牧兽医 | 11371篇 |
园艺 | 5151篇 |
植物保护 | 3291篇 |
出版年
2024年 | 472篇 |
2023年 | 1441篇 |
2022年 | 3489篇 |
2021年 | 3169篇 |
2020年 | 3048篇 |
2019年 | 3115篇 |
2018年 | 2096篇 |
2017年 | 3591篇 |
2016年 | 2249篇 |
2015年 | 3530篇 |
2014年 | 3623篇 |
2013年 | 4459篇 |
2012年 | 6151篇 |
2011年 | 6355篇 |
2010年 | 5962篇 |
2009年 | 5054篇 |
2008年 | 5167篇 |
2007年 | 4851篇 |
2006年 | 3929篇 |
2005年 | 3111篇 |
2004年 | 1957篇 |
2003年 | 1248篇 |
2002年 | 1235篇 |
2001年 | 1158篇 |
2000年 | 1022篇 |
1999年 | 375篇 |
1998年 | 39篇 |
1997年 | 16篇 |
1996年 | 14篇 |
1995年 | 21篇 |
1994年 | 15篇 |
1993年 | 18篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 7篇 |
1986年 | 13篇 |
1985年 | 2篇 |
1981年 | 7篇 |
1966年 | 2篇 |
1965年 | 2篇 |
1962年 | 12篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1957年 | 3篇 |
1956年 | 34篇 |
1955年 | 12篇 |
1953年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
981.
982.
983.
建立莜麦籽粒产量、生物产量、籽粒蛋白质产量、总蛋白质产量与施氮总量及追施比例之间的效应方程,求解不同边际利润下的最佳施氮量及追施比例。结果表明施氮量改变,直接影响最佳追施比例、籽粒产量、蛋白质产量和生物产量等,施氮量在17.25~120.75kg/hm2区间内,各种目标产量随施氮量的增加而稳定增加,在合理的施氮量区间内实现既定产量,施氮总量与追施比例可以消长互替,降低追施比例则增加氮素总量,或增加追施比例则可以减少氮素总量。得出了不同目标产量时的最佳氮肥用量与追施比例和对应于氮肥不同用量的最佳追施比例及理论产量的动态施肥模式的数学方程。 相似文献
984.
Peixin YANG Mohamed S. MEDAN Koji Y. ARAI Wanzhu JIN Gen WATANABE Kazuyoshi TAYA 《Animal Science Journal》2005,76(5):427-434
The ontogeny of testicular inhibin/activin in ducks was investigated. Testicular localization of three inhibin/activin subunits (α, βA and βB) was determined in embryonic and newly hatched ducks from 12 days of incubation to 1 day of age, in immature ducks and in adult ducks. In the duck embryonic testis, positive α‐subunit immunostaining was first detected in the Leydig cells and Sertoli cells on day 15 of incubation, whereas βA‐subunit and βB‐subunit immunostaining were found in Sertoli cells and primary germ cells on day 18 of incubation. In 1 month old ducks, intense staining of α‐subunit was present in the seminiferous epithelium consistent with localization in Sertoli cells and primary germ cells, and the immunostaining of the βA‐ and βB‐subunit was also present in Sertoli cells and primary germ cells. Specific immunostaining with inhibin/activin α‐, βA‐ and βB‐subunits antisera occurred in Sertoli cells in the adult duck testes. In conclusion, it was shown that, in the duck testis, the majority of α‐, βA‐ and βB‐subunits are colocalized in Sertoli cells with a certain degree of staining in germ cells and the α‐subunit is present in Leydig cells of embryonic testes before day 18 of incubation. These results indicate that Sertoli cells and possibly germ cells in the embryonic testes of late stage of incubation and newly hatched ducks, immature ducks and mature ducks may produce bioactive inhibin dimers, inhibin A and inhibin B, as a possible regulator of follicle‐stimulating hormone secretion. Free inhibin/activin subunits and their dimers may also play an autocrine/paracrine role in the development of the testis and spermatogenesis. Furthermore, early onset of the α‐subunit in duck testes indicates that it may have an autocrine/paracrine effect on steroid hormones, which is important for sex differentiation. 相似文献
985.
GUO Wen-yi YANG Yong JIA Guo-liang ZHANG Rong-qing ZHANG Qing LI Jing-xia GAO Hao-kao 《园艺学报》2005,21(1):72-76
AIM: To examine the effects of L-carnitine on apoptosis and oxidant injury in cultured neonatal rat cardiomyocytes induced by hypoxia/reoxygenation and its possible mechanism. METHODS: The cultured cardiomyocytes were divided into three groups, control, A/R group (anoxia for 120 min, reoxygenation for 240 min) and L-carnitine treatment group, in which cells were exposed to 20 mg/L, 50 mg/L, 100 mg/L, 200 mg/L L-carnitine respectively at 2 h before anoxia. The superoxide dismutase (SOD), succinate dehydrogenase (SDH) activities and malondialdehyde (MDA) content were examined, and the apoptosis was determined by flow of cytometry (FCM). In addition, the ultrastructure was observed by transmission electron microscopy. RESULTS: In A/R group, SOD and SDH activities were lower, the apoptosis rate and MDA content were higher than those in control group (P<0.05). In L-carnitine treatment group, SOD and SDH activities were higher, the apoptosis rate and MDA content were lower than those in A/R group, a L-carnitine concentration-dependent effect was found. Moreover, impairment of myocardial ultrastructure was more severe in A/R group than L-carnitine treatment group. CONCLUSION: L-carnitine can protect cardiomyocytes against hypoxia/reoxygenation-induced injury in a dose-dependent manner. 相似文献
986.
CAI Wei-bin YANG Zhong-han LI Chao-yang SONG Zhi-hong ZHOU Shi-hao LUO Xiao-feng GAO Guo-quan 《园艺学报》2005,21(4):652-656
AIM: To observe the effects of ginkgolide B on the neuron apoptosis induced by glutamate and explore whether this effects are related to the changes of calcium in neurons. METHODS: Primary neuron culture was prepared according to a previously reported procedure with slight modification. Neuron damage was induced by 0.8 mmol/L glutamate. The cell survival rate was examined by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assays. The neuron morphological changes, Hoechst 33258 unclear-staining analysis and agarose gel electrophoresis of DNA were measured as the indexes of cell apoptosis. Intracellular free Ca2+ concentration in neurons was measured by using the fluorescent Ca2+ indicator Fura-2/AM. RESULTS: The cells, exposed to glutamate (0.8 mmol/L), showed characteristic change of apoptosis and calcium overload, which were relieved by the treatment of ginkgolide B (10-250 μmol/L), with survival increasing and cell morphology restoring and DNA fragment decreasing. CONCLUSIONS: Ginkgolide B prevents the neurons from glutamate neurotoxicity by inhibiting glutamate-induced apoptosis. The potential mechanism of its action may be related to the competitive PAF receptor binding of ginkgolide B and decreasing the intracellular calcium concentration in neurons. 相似文献
987.
ZHAO Ya-jun XU Chang-qing SHI Sa SUN Hong-li WANG Ning LI Bao-xin WANG Ling YANG Bao-feng Rui Wang 《园艺学报》2005,21(10):1938-1941
AIM: To study the effect of extrogenous low concentration polyamine on cardiomyocyte calcium overload caused by anoxia and reoxygenation. METHODS: Enzymatically isolated rat ventricular myocytes were perfused with normal Tyrode solution for 8 min, then change to anoxia solution for 32 min, at last back to normal Tyrode solution perfusion for 8 min to establish the cardiomyocyte model of anoxia and reoxygenation. Spermine was added extracellularly to the bath before anoxia and spermine, spermidine or putrescine was added extracellularly after reoxygenation. Intracellular calcium fluorescence intensity (FI) was measured continuously by laser scan confocal microscope (LSCM). RESULTS: In the unstimulated state, exogenous spermine (1 mol/L) did not change resting [Ca2+]i in the rat cardiomyocytes. Adding spermine before anoxia antagonized the [Ca2+]i elevating caused by anoxia/reoxygenation. Adding spermine after reoxygenation also lowed the enhanced [Ca2+]i caused by reoxygenation. Considering the potency of two conditions, the former was more efficacious than the later. Spermidine and putrescine also lowed the enhanced [Ca2+]i caused by reoxygenation, but they were less efficacious than spermine. CONCLUSIONS: The results indicate that spermine given before anoxia or after reoxygenation, antagonized or lowed the cardiomyocytes calcium overload caused by anoxia/reoxygenation, but the later was weaker than the former. The order of potency of the polyamine lighten cardiomyocytes calcium overload caused by anoxia/reoxygenation was spermine>spermindine>putrescine. 相似文献
988.
AIM: To investigate if beta2-adrenergic receptors result in more Ca2+ load after myocardial infarction (MI), the effects of beta2-adrenergic blocker on cytosolic Ca2+ ([Ca2+]i) were studied. METHODS: Male Wistar rats underwent a ligation of left coronary artery (n=9) or a sham operation (n=3). Cardiomyocytes were dissociated at 2, 4 and 8 weeks after MI and [Ca2+]i was measured via fura-2 fluorescence. The response of cardiomyocytes to isoproterenol (1 μmol/L) in the presence or absence of atenolol (1 μmol/L), beta2-adrenergic blocker ICI118,551 (0.1 μmol/L) or propranolol (1 μmol/L) was examined. RESULTS: ICI118,551 suppressed the increase in [Ca2+]i induced by isoproterenol at 4 and 8 weeks after MI (24.5%±5.7% vs 57.8%±13.2%, P<0.01; 12.2%±7.9% vs 44.6%±11.3%, P<0.01), but had no effects in control and 2 weeks post-MI groups. It decreased [Ca2+]i in control and the three post-MI groups by 14.3%, 7.9%, 57.6% and 72.6%, respectively. Atenolol had suppressive effects only in control and 2 weeks post-MI groups (P<0.05). Propranolol had suppressive effects in control and all three post-MI groups (P<0.01). CONCLUSION: Beta 2-adrenergic blocker ICI118,551 exerts negative effects on [Ca2+]i after MI, and the effects dramatically increase with the progression of MI. 相似文献
989.
ZHANG Zhan JIA Li-ting HOU Lei WANG Xue-mei CHANG Cai-hong YANG Ru-jing ZHANG Xi LIU Sheng-hong ZHENG Fang GONG Fei-li 《园艺学报》2005,21(12):2457-2461
AIM: To detect the effects of NK cells on the etiology of severe pre-eclampsia. METHODS: The peripheral blood and umbilical blood from severe pre-eclamptic patients and normal late pregnant women were collected. NK cells were seperated in percoll and counted by SAP. The proliferating ability of NK cells was measured by MTT and killing power of NK cells was determined by [51Cr] releasing test. The immunohistochemistry method was used to detect the quantity of NK cells and the expression of HLA-G in placenta of them. RESULTS: (1) Compared with that in normal late pregnant women, the counts of the NK cells in peripheral blood, umbilical blood and decidua of severe pre-eclamptic patients were significantly higher (all P<0.05). (2) Compared with that in normal late pregnant women, proliferating and killing ability of NK cells in peripheral blood and umbilical blood of severe pre-eclamptic patients were significantly higher. (3) The expression of HLA-G protein in placenta of severe pre-eclampsia group was lower than that in normal group (P<0.05). CONCLUSION: The quantity of NK cells in severe pre-eclamptic patients is increased with stronger biologic function. They may be related with the pathogenesis of severe pre-eclampsia. 相似文献
990.