全文获取类型
收费全文 | 8377篇 |
免费 | 1725篇 |
国内免费 | 1192篇 |
专业分类
11294篇 |
出版年
2024年 | 109篇 |
2023年 | 399篇 |
2022年 | 417篇 |
2021年 | 601篇 |
2020年 | 538篇 |
2019年 | 500篇 |
2018年 | 407篇 |
2017年 | 429篇 |
2016年 | 369篇 |
2015年 | 376篇 |
2014年 | 456篇 |
2013年 | 632篇 |
2012年 | 358篇 |
2011年 | 403篇 |
2010年 | 326篇 |
2009年 | 429篇 |
2008年 | 416篇 |
2007年 | 447篇 |
2006年 | 390篇 |
2005年 | 343篇 |
2004年 | 307篇 |
2003年 | 293篇 |
2002年 | 242篇 |
2001年 | 221篇 |
2000年 | 173篇 |
1999年 | 181篇 |
1998年 | 144篇 |
1997年 | 115篇 |
1996年 | 121篇 |
1995年 | 106篇 |
1994年 | 105篇 |
1993年 | 82篇 |
1992年 | 86篇 |
1991年 | 84篇 |
1990年 | 59篇 |
1989年 | 59篇 |
1988年 | 48篇 |
1987年 | 49篇 |
1986年 | 38篇 |
1985年 | 63篇 |
1984年 | 55篇 |
1983年 | 36篇 |
1982年 | 57篇 |
1981年 | 35篇 |
1980年 | 34篇 |
1979年 | 24篇 |
1978年 | 35篇 |
1977年 | 30篇 |
1976年 | 19篇 |
1975年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
松树蜂与其共生真菌的互利共生关系 总被引:3,自引:0,他引:3
松树蜂Sirex noctilio Fabricius是一种重要的国际林业检疫性害虫,主要危害针叶树,原产欧亚大陆和北非。近100多年来,先后入侵大洋洲(新西兰和澳大利亚)、南美洲(乌拉圭、阿根廷、巴西和智利)、北美洲(加拿大和美国),以及南非。2013年8月,在中国黑龙江省内首次发现松树蜂,目前发现其主要危害樟子松。松树蜂能与一种淀粉韧革菌属Amylostereum的真菌Amylostereum areolatum(Fr.)Boidin形成严格的互利共生关系,该虫除直接钻蛀树木外,还能通过产卵行为将自身毒素腺体分泌的毒素和体内共生真菌随同虫卵一起注入寄主树木体内,形成"虫-毒-菌"3个致害因子相互协作的特殊危害方式,加速树势的衰弱并造成寄主树木死亡。本文就国内外松树蜂与其共生菌互利共生关系的研究进行了综述,分别从结构与功能的层次上对其互利共生关系进行了梳理和总结,重点阐释了松树蜂与共生菌的营养共生关系,松树蜂携带传播共生菌的机制,共生菌的种群遗传学以及松树蜂毒素和共生菌在危害寄主树木时的协同关系等。以期为开展关于松树蜂的专项研究提供一些合理的建议,同时为积极有效地防控该害虫提供科学依据。 相似文献
72.
土壤原生动物群落及其生态功能 总被引:8,自引:0,他引:8
土壤原生动物是土壤微生物区系的重要组成部分。在土壤生态系统中 ,由于微生物与微动物的生命活动及其相互作用 ,从而形成了土壤的物质循环和能量转化。土壤原生动物既参与了微生物所介导的物质转化和能量循环 ,又参与了动物对微生物的捕食作用。由于原生动物具有丰富的种类和多样性以及巨大的生物量 ,所以土壤原生动物的群落及其生态功能 ,已引起了人们的广泛关注 ,并且研究理论与方法日益深入。但我国在这方面的研究报道较少 ,本文拟从群落与生态功能方面的进展做一概述。1 土壤原生动物的群落特征土壤与淡水原生动物最早是由Anton… 相似文献
73.
《植物分类与资源学报》2006,1(1):69-77
WRKY 蛋白质是一个植物特有的超级转录调控因子家族, 在拟南芥和水稻基因组中分别拥有至少74 个和97 个成员。最古老的WRKY 转录调控因子拥有2 个高度保守的WRKY 结构域, 可能起源于15~ 20 亿年前的真核生物。虽然所有WRKY 蛋白质主要通过特异地结合靶基因启动子区域的W 盒序列而调控其表达, 但各家族成员基因的生物学功能存在着各自的特异性。本文详细总结了WRKY 蛋白质在调控植物发育和逆境诱导反应的信号转导途径建立等方面的分子生物学功能。 相似文献
74.
75.
《基因组蛋白质组与生物信息学报(英文版)》2016,(4):244-252
The search for a parameter representing left ventricular relaxation from non-invasive and invasive diagnostic tools has been extensive, since heart failure (HF) with preserved ejection fraction (HF-pEF) is a global health problem. We explore here the feasibility using patient-specific cardiac computer modeling to capture diastolic parameters in patients suffering from different degrees of systolic HF. Fifty eight patients with idiopathic dilated cardiomyopathy have undergone thorough clinical evaluation, including cardiac magnetic resonance imaging (MRI), heart catheterization, echocardiography, and cardiac biomarker assessment. A previously-introduced framework for creating multi-scale patient-specific cardiac models has been applied on all these patients. Novel parameters, such as global stiffness factor and maximum left ventricular active stress, representing cardiac active and passive tissue properties have been computed for all patients. Invasive pressure measurements from heart catheterization were then used to evaluate ventricular relaxation using the time constant of isovolumic relaxation Tau (s). Parameters from heart catheterization and the multi-scale model have been evaluated and compared to patient clinical presentation. The model parameter global stiffness factor, representing diastolic passive tissue properties, is correlated signif-icantly across the patient population with s. This study shows that multi-modal cardiac models can successfully capture diastolic (dys) function, a prerequisite for future clinical trials on HF-pEF. 相似文献
76.
77.
Vijayakumar Maheshwari Malathi Sushil K. Jalali Dandinashivara K. Sidde Gowda Muthugounder Mohan Thiruvengadam Venkatesan 《Insect Science》2017,24(1):35-46
The brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the major pests of rice throughout Asia. Extensive use of insecticides for suppressing N. lugens has resulted in the development of insecticide resistance leading to frequent control failures in the field. The aim of the present study was to evaluate resistance in the field populations of N. lugens from major rice growing states of South India to various insecticides. We also determined the activity of detoxifying enzymes (esterases [ESTs], glutathione S‐transferases [GSTs], and mixed‐function oxidases [MFOs]). Moderate levels of resistance were detected in the field populations to acephate, thiamethoxam and buprofezin (resistance factors 1.05–20.92 fold, 4.52–14.99 fold, and 1.00–18.09 fold, respectively) as compared with susceptible strain while there were low levels of resistance to imidacloprid (resistance factor 1.23–6.70 fold) and complete sensitivity to etofenoprox (resistance factor 1.05–1.66 fold). EST activities in the field populations were 1.06 to 3.09 times higher than the susceptible strain while for GST and MFO the ratios varied from 1.29 to 3.41 and 1.03 to 1.76, respectively. The EST activity was found to be correlated to acephate resistance (r = 0.999, P ≥ 0.001). The high selection pressure of organophosphate, neonicotinoid, and insect growth regulator (IGR) in the field is likely to be contributing for resistance in BPH to multiple insecticides, leading to control failures. The results obtained will be beneficial to IPM recommendations for the use of effective insecticides against BPH. 相似文献
78.
79.
鹿血对小鼠肠道菌群及免疫功能的影响 总被引:4,自引:0,他引:4
本实验以肠道菌群检测与免疫不腹腔Mψ吞噬功能测定,溶血空斑试验,淋巴细胞转化试验,NK细胞活性测定等方法,初步研究了中药鹿血对抗生素造成的菌群失调性腹泻小鼠肠道菌菌及免疫功能的影响。 相似文献
80.
AIMS: To exploit conidiospores of Aspergillus niger as a vector for glucose oxidase extraction from solid media, and their direct use as biocatalyst in the bioconversion of glucose to gluconic acid. METHODS AND RESULTS: Spores of A. niger (200 h old) were shown to fully retain all the glucose oxidase synthesized by the mycelium during solid-state fermentation (SSF). They acted as catalyst and carried out the bioconversion reaction effectively, provided they were permeabilized by freezing and thawing. Glucose oxidase activity was found retained in the spores even after repeated washings. Average rate of reaction was 1.5 g l(-1) h(-1) with 102 g l(-1) of gluconic acid produced out of 100 g l(-1) glucose consumed after approx. 100 h reaction, which corresponded to a molar yield close to 93%. These results were obtained with permeabilized spores in the presence of a germination inhibitor, sodium azide. CONCLUSIONS: Spores of A. niger served as efficient catalyst in the model bioconversion reaction after permeabilization. SIGNIFICANCE AND IMPACT OF THE STUDY: To our knowledge, this is the first detailed study on the ability of A. niger spores to act as reservoir of enzyme synthesized during SSF without its release into solid media. Use of this material served as an innovative concept for enzyme extraction and purification from a solid medium. Moreover, this approach could compete efficiently with the conventional use of mycelial form of the fungus in gluconic acid production. 相似文献