全文获取类型
收费全文 | 3351篇 |
免费 | 232篇 |
国内免费 | 445篇 |
出版年
2023年 | 35篇 |
2022年 | 55篇 |
2021年 | 61篇 |
2020年 | 49篇 |
2019年 | 61篇 |
2018年 | 49篇 |
2017年 | 45篇 |
2016年 | 46篇 |
2015年 | 58篇 |
2014年 | 87篇 |
2013年 | 108篇 |
2012年 | 141篇 |
2011年 | 121篇 |
2010年 | 134篇 |
2009年 | 182篇 |
2008年 | 190篇 |
2007年 | 142篇 |
2006年 | 121篇 |
2005年 | 113篇 |
2004年 | 75篇 |
2003年 | 68篇 |
2002年 | 38篇 |
2001年 | 39篇 |
2000年 | 42篇 |
1999年 | 47篇 |
1998年 | 56篇 |
1997年 | 52篇 |
1996年 | 42篇 |
1995年 | 41篇 |
1994年 | 27篇 |
1993年 | 22篇 |
1992年 | 37篇 |
1990年 | 23篇 |
1989年 | 26篇 |
1987年 | 27篇 |
1985年 | 22篇 |
1983年 | 24篇 |
1981年 | 27篇 |
1979年 | 21篇 |
1959年 | 53篇 |
1958年 | 130篇 |
1957年 | 140篇 |
1956年 | 140篇 |
1955年 | 154篇 |
1954年 | 154篇 |
1953年 | 122篇 |
1952年 | 113篇 |
1951年 | 106篇 |
1950年 | 66篇 |
1948年 | 25篇 |
排序方式: 共有4028条查询结果,搜索用时 312 毫秒
991.
大鼠胰腺发育不同阶段基因表达分析 总被引:1,自引:0,他引:1
目的:探讨大鼠胰腺发育不同阶段基因表达规律.方法:运用高通量基因芯片技术检测大鼠胰腺从胚胎12.5天(E12.5)到成年不同时期基因表达情况.结果:基因芯片所涵盖的基因59%在E12.5有表达,65%在15.5有表达,63%在E18.8有表达,53%在新生胰腺中有表达,38%在成年胰腺中有表达.E18.5相对于E15.5表达上调的基因中代谢相关的酶类有121条,占上调基因的18.2%,E18.5相对于E15.5表达下调的基因主要是一些转录因子和骨架蛋白.结论:在大鼠胰腺的发育过程中,早中期以细胞分化为主,而后期则是以细胞功能成熟为主. 相似文献
992.
目的:研究不同剂量的阿托伐他汀治疗冠状动脉粥样硬化性心脏病的疗效,并探讨性别与年龄对疗效的影响.方法:将320例冠状动脉粥样硬化性心脏病患者随机分为4组(每组80例):10mg/d阿托伐他汀治疗A组、40mg/d阿托伐他汀治疗B组、80mg/d阿托伐他汀治疗C组与常规治疗D组,其中常规治疗组采用硝酸甘油、血管紧张与素转换酶抑制剂阿司匹林等;疗程12周.分析比较各组患者治疗前后:TG、TC、HDL-C、LDL-C和hs-CRP的水平变化.结果:治疗12周后,与常规治疗组相比:①三个不同剂量的阿托伐他汀治疗组中患者的TG、TC、HDL-C、LDL-C和hs-CRP分子的浓度变化差异均有统计学意义,P<0.05;其中以剂量为40 mg/d的阿托伐他汀治疗组的整体疗效相对最好,P<0.05;②治疗效果与患者年龄呈负相关趋势;③在45-55岁这个年龄阶段,女性患者的治疗效果要好于同年龄阶段的男性患者,P<0.05;④在老年患者中,大剂量的阿伐他汀的安全性明显低于中小剂量组.结论:中等剂量的阿托伐他汀对冠状动脉粥样硬化性心脏病的疗效显著,安全性良好. 相似文献
993.
首次报道了南方山荷叶大、小孢子发生和雌、雄配子体形成。主要结果如下:花药4室,花药壁发育为基本型,由7层细胞组成,由外到内依次为表皮、药室内壁、3层中层和2层绒毡层;药室内壁有带状加厚现象,绒毡层细胞多具双核,为腺质型绒毡层;多孢原,发生于表皮下;小孢子母细胞减数分裂为同时型,小孢子四分体多为四面体型,少数为十字交叉形、直线形、左右对称形或"T"形;成熟花粉粒为2-细胞型,偶见3-细胞型;成熟花粉粒呈圆形,具单萌发孔。雌蕊1枚,子房单心皮,纵切面呈瓶状;1室,边缘胎座,具4~5枚发育不同步的横生胚珠。胚珠具双珠被,厚珠心;珠孔由两层珠被共同形成,在一直线上或呈"之"字形。多孢原,位于珠心表皮下。直线形四分体,合点端的1个大孢子发育为功能大孢子,胚囊发育为蓼型。成熟胚囊中,3个反足细胞大而明显,但宿存时间短,较早退化。 相似文献
994.
The family of Tephritid fruit flies (Tephritidae, Diptera) is composed of more than 4000 species and more than 350 are of economic importance (EI). The Tephritid Barcoding Initiative (TBI) aims at obtaining DNA barcodes for all EI species and the majority of their congeners. Dry pinned specimens from natural history collections are an important resource for reference material, but were often collected decades ago. We observed a strong decrease in the success rate of obtaining a full COX1 DNA barcode (658 bp), with an increasing age of the specimens. Obtaining full barcodes is often not possible using standard protocols. We developed a universal Tephritid primer set for multiple overlapping mini-barcodes that allows reconstructing the full COX1 DNA barcode. These newly developed primers and the corresponding protocol will facilitate the utilization of the extensive natural history collection by the TBI consortium. 相似文献
995.
胎膜组织贴壁细胞:一种新的间质干细胞来源 总被引:1,自引:1,他引:0
[目的] 建立体外分离纯化胎膜组织贴壁细胞(fetal membrane derived adherent cells,FMDACs)的方法,并且研究FMDACs的基本生物学特性。[方法] 用胰酶消化法分离FMDACs,体外传代培养,并进行向成骨、成脂细胞的诱导分化培养,流式细胞仪、免疫细胞化学检测表面抗原,核型分析及致瘤性实验。[结果] 成功地进行了FMDACs的原代培养及传代培养,FMDACs具有良好的增殖能力,表达CD44、CD29,不表达CD34、CD14、CD45,经诱导后能够分化为成骨细胞和成脂细胞,传代多次后核型正常,无致瘤性。[结论] 胎膜组织中可以分离得到具有间质干细胞特性的贴壁细胞,具有较强的自我更新和多向分化能力,遗传背景稳定无致瘤性。FMDACs为临床应用进行细胞治疗和基因治疗提供了新的来源。 相似文献
996.
ARNOLD DE LOOF ILSE CLAEYS GERT SIMONET PETER VERLEYEN TIM VANDERSMISSEN FILIP SAS JURGEN HUYBRECHTS 《Insect Science》2006,13(1):3-12
The changes accompanying the transition from the gregarious to the solitary phase state in locusts are so drastic that for a long time these phases were considered as distinct species. It was Boris Uvarov who introduced the concept of polyphenism. Decades of research revealed that phase transition implies changes in morphometry, the color of the cuticle, behavior and several aspects of physiology. In particular, in the recent decade, quite a number of molecular studies have been undertaken to uncover phase-related differences. They resulted in novel insights into the role of corazonin, neuroparsins, some protease inhibitors, phenylacetonitrile and so on. The advent of EST-databases of locusts (e.g. Kang et al., 2004) is a most encouraging novel development in physiological and behavioral locust research. Yet, the answer to the most intriguing question, namely whether or not there is a primordial molecular inducer of phase transition, is probably not within reach in the very near future. 相似文献
997.
J. K. J. VAN HOUDT B. HELLEMANS A. VAN DE PUTTE P. KOUBBI F. A. M. VOLCKAERT 《Molecular ecology resources》2006,6(1):157-159
Six polymorphic microsatellites were isolated from the dusky notothen, Trematomus newnesi (Boulenger 1902), using a microsatellite enrichment protocol and selective hybridization with di‐ tetra‐ and penta‐repeat probes. The loci were screened in 48 individuals captured in the Southern Ocean (coastal zone of Terre‐Adélie), revealing eight to 22 alleles per locus and an observed heterozygosity ranging from 0.70 to 0.92. These microsatellite markers provide a tool to study the relationship between the various morphs observed in this species and can be used for population genetic analysis and biodiversity studies. 相似文献
998.
Comparison of Single and Touchdown PCR Protocols for Detecting Pneumocystis jirovecii DNA in Paraffin-Embedded Lung Tissue Samples 总被引:1,自引:0,他引:1
999.
1000.
WENDEL J. TELES PONTES ERALDO RODRIGUES LIMA ERIVELTON G. CUNHA PEDRO M. TEIXEIRA DE ANDRADE AILTON PINHEIRO LÔBO REGINALDO BARROS 《Physiological Entomology》2010,35(2):134-139
Recognition and acceptance of a suitable host plant by phytophagous insects requires the integration of visual, physical and chemical cues. The present study investigates the host cues that a specialist insect integrates to optimize oviposition decisions and whether these cues are weighted in a specific way. The study also determines whether the tomato fruit borer Neoleucinodes elegantalis (Guenée) (Lepidoptera: Crambidae), an important pest on Solanaceae in Brazil, shows a preference for oviposition sites that differ in physical and/or chemical cues. When styrofoam balls are provided as artificial fruits, N. elegantalis deposit significantly more eggs on rough artificial fruits than on smooth ones. Hexane fruit extracts applied to the artificial fruits stimulate female oviposition strongly. Physical and chemical cues also affect the oviposition of females when offered together. Furthermore, certain parts of the artificial fruits are prefered, irrespective of the presence of chemical cues. Both physical and chemical cues affect oviposition decisions; hence, the fruit borer relies on cues of different sensory modalities. 相似文献