全文获取类型
收费全文 | 17167篇 |
免费 | 1858篇 |
国内免费 | 5068篇 |
专业分类
24093篇 |
出版年
2024年 | 129篇 |
2023年 | 383篇 |
2022年 | 648篇 |
2021年 | 912篇 |
2020年 | 734篇 |
2019年 | 862篇 |
2018年 | 778篇 |
2017年 | 643篇 |
2016年 | 764篇 |
2015年 | 1092篇 |
2014年 | 1383篇 |
2013年 | 1379篇 |
2012年 | 1780篇 |
2011年 | 1525篇 |
2010年 | 1128篇 |
2009年 | 999篇 |
2008年 | 1221篇 |
2007年 | 1119篇 |
2006年 | 975篇 |
2005年 | 892篇 |
2004年 | 739篇 |
2003年 | 713篇 |
2002年 | 612篇 |
2001年 | 464篇 |
2000年 | 441篇 |
1999年 | 309篇 |
1998年 | 180篇 |
1997年 | 109篇 |
1996年 | 109篇 |
1995年 | 119篇 |
1994年 | 84篇 |
1993年 | 63篇 |
1992年 | 86篇 |
1991年 | 71篇 |
1990年 | 53篇 |
1989年 | 51篇 |
1988年 | 60篇 |
1987年 | 32篇 |
1986年 | 35篇 |
1985年 | 33篇 |
1984年 | 34篇 |
1983年 | 23篇 |
1982年 | 30篇 |
1981年 | 20篇 |
1976年 | 15篇 |
1973年 | 21篇 |
1972年 | 13篇 |
1966年 | 13篇 |
1958年 | 14篇 |
1957年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
从研究生"高级微生物学"课程的定位、研究生学习该课程的目的、知识背景差异及教学过程中的问题等方面分析了目前研究生"高级微生物学"教学中存在的问题。通过教学内容的优化、教材建设、教学方法改革、师资队伍建设以及建立师生交流平台等方面进行教学改革实践,取得了较好的教学效果。 相似文献
14.
Orbilia Fr. and Hyalorbilia Baral & G. Marson are the only genera currently accepted in the family Orbiliaceae which was established by Nannfeldt (Baral, 1994; Kirk et al., 2001). Hyalorbilia was erected by Baral and Marson (2001) based on unstalked asci arising from crosiers, with hemispherical apices without wall thickenings, some bipolar-symmetrical globose inclusion bodies in ascospores (living state), asci and paraphyses cohere in a gelatinous matrix, paraphyses with not or only slightly inflated apices, and an ectal excipulum of horizontally oriented textura rectangular. 相似文献
15.
It was well known that beta-amyloid (Abeta) and tau protein play an important role in pathological procedure of Alzheimer's disease (AD), a senile dementia. The growth inhibitory factor (GIF, also named metallothionein-3, MT-3) had been demonstrated to inhibit the outgrowth of cortex neurons in the medium with extract of the AD patient brain. In our experiments, it was found that the neurons of cortex and the PC12 (pheochromocytoma) cells could be protected from the cytotoxicity of beta-amyloid 25-35 in presence of GIF and its domains. Additionally, GIF can scavenge the hydroxyl radical efficiently in CytC-VitC radical producing system and its alpha-domain shown more effective potentials than its beta-domain. The electron paramagnetic resonance spectra also show that the alpha-domain has more potential ability for eliminating reactive oxygen free radicals than its beta-domain. The results suggest that GIF could act as an efficient scavenger against free radicals in vitro and the alpha-domain in GIF molecule shows more potential in protecting against reactive oxygen species injury than the beta-domain. 相似文献
16.
Sporopollenin layers in the cell wall of coccal green algae are responsible for the resistance of cell walls to destructive processes during fossilization as well as during chemical preparation of samples for pollen-analysis. Pollen slides of samples from limnic sediments thus also contain some algal cell walls. Although some pollen-analysts tried to stress this fact, the finds of algae in pollen slides have not been paid systematic attention yet, despite their potential use for a more accurate palaeoecological reconstruction. The article summarizes the results of palaeoecological studies showing how the algae can be used in palaeoecological reconstruction of past environments. The possibility of utilizing the indicative value of algal finds is demonstrated on examples of algal communities from fossil, subrecent and recent sediments from different longitudes, latitudes, and altitudes. The identification and indicative values of species and varieties ofPediastrum are included in a special review (Komárek &; Jankovská, Biblioth. Phycol., in press). The contemporary knowledge of ecological requirements of the given taxa, completed by information from their fossil finds, makes possible the reconstruction of trophic and temperature conditions and of the purity of the water environment of the past water biotopes. 相似文献
17.
大葱组织培养中玻璃苗特性研究 总被引:4,自引:1,他引:4
以章丘大葱为试验材料,从形态组织学及生理生化等方面探讨了大葱试管苗玻璃化发生的可能机理。结果表明,玻璃苗形态组织结构与正常苗有很大差异,玻璃苗组织含水量增加,过氧化物酶(POD)活性增强,叶绿素总量、叶绿素a、叶绿素b、过氧化氢酶(CAT)的活性、可溶性蛋白含量均降低。玻璃苗酯酶同工酶谱带与正常苗相比,增加了一条带,同时缺少了两条带;可溶性蛋白电泳分析表明,玻璃苗与正常苗间也存在明显差异。可见,当外界环境条件不适宜植物生长需要时,植物体在基因表达水平上将会受到影响,表达产物的差异可引起生理代谢功能上的紊乱,从而导致形态结构的畸型,进而产生玻璃化苗。 相似文献
18.
鄱阳湖生态经济区生态系统服务价值预测与驱动力 总被引:6,自引:0,他引:6
鄱阳湖生态经济区是我国第一个上升到国家战略的生态经济区。利用鄱阳湖生态经济区2004、2008、2012、2016年的MODIS数据,获得4个对应期的土地利用/覆盖数据,参照修订的单位面积生态系统服务价值当量表与灰色GM(1,1)模型,预测了2016-2024年(间隔2 a)的生态系统服务价值数据,并对引起生态服系统务价值变化的驱动力进行了分析。结果表明,鄱阳湖生态经济区在2004-2016年间,草地、建设用地和未利用地面积增加,耕地、林地、水域面积减少,但2016-2024年的预测值变化率仅为-0.17%,表明该研究区生态系统服务价值即将进入一个相对稳定的状态;驱动力分析表明,人为综合干扰在空间分布上以中等影响强度干扰为主,城镇化率是区域总生态系统服务价值降低的首要驱动力,其次分别为非农业人口、人口密度、第一产业GDP、第二产业GDP、固定资产投资额、总GDP及第三产业GDP。建议加强土地利用规划与调控,控制城镇化建设用地扩展,调整产业结构、降低污染,促进鄱阳湖生态经济区总生态系统服务价值的提升。 相似文献
19.
So Eun Park Jong Cheol Kim Se Jin Lee Mi Rong Lee Sihyeon Kim Dongwei Li Sehyeon Baek Ji Hee Han Jeong Jun Kim Kyung Bon Koo Tae Young Shin Jae Su Kim 《Journal of Asia》2018,21(4):1102-1109
Entomopathogenic fungi have great potential to control agricultural and horticultural insect pests, however optimizing conidial production systems to demonstrate high productivity and stability still needs additional efforts for successful field application and industrialization. Although many virulent entomopathogenic fungal isolates have been viewed as potential candidates in a laboratory environment, very few of the isolates are being used in practice for application in agricultural fields as commercial products. I. javanicus is an entomopathogenic fungus that is parasitic to various diverse coleopteran and lepidopteran insects and thought good candidate as biopesticdes. In this work, the basic characteristics of two entomopathogenic fungi, I. javanica FG340 and Pf04, were investigated in morphological examinations, genetic identification, and virulence against Thrips palmi, and then the feasibility of various grains substrates for conidial production was assessed, particularly focusing on conidial productivity and thermotolerance. Isaria javanica FG340 and Pf04 conidia were solid-cultured on 12 grains for 14?days in a Petri dish. Of the tested Italian millet, perilla seed, millet and barley-based cultures showed high conidial production. The four-grain media yielded >1?×?109 conidia/g of I. javanica FG340 and Pf04. Pf04 strain had enhanced thermotolerance up to 45?°C when cultured on Italian millet. In application, it was easy to make a conidial suspension using the cultured grains, and several surfactants were tested to release the conidia. This work suggests several possible inexpensive grain substrates by which to promote conidial production combined with enhanced stability against exposure to high temperature. 相似文献
20.