全文获取类型
收费全文 | 5610篇 |
免费 | 519篇 |
国内免费 | 652篇 |
专业分类
6781篇 |
出版年
2024年 | 22篇 |
2023年 | 104篇 |
2022年 | 229篇 |
2021年 | 334篇 |
2020年 | 266篇 |
2019年 | 333篇 |
2018年 | 247篇 |
2017年 | 197篇 |
2016年 | 245篇 |
2015年 | 345篇 |
2014年 | 412篇 |
2013年 | 420篇 |
2012年 | 547篇 |
2011年 | 460篇 |
2010年 | 278篇 |
2009年 | 257篇 |
2008年 | 279篇 |
2007年 | 233篇 |
2006年 | 194篇 |
2005年 | 191篇 |
2004年 | 161篇 |
2003年 | 164篇 |
2002年 | 134篇 |
2001年 | 107篇 |
2000年 | 83篇 |
1999年 | 66篇 |
1998年 | 47篇 |
1997年 | 40篇 |
1996年 | 39篇 |
1995年 | 33篇 |
1994年 | 31篇 |
1993年 | 29篇 |
1992年 | 35篇 |
1991年 | 20篇 |
1990年 | 20篇 |
1989年 | 20篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1974年 | 5篇 |
1973年 | 8篇 |
1972年 | 13篇 |
1971年 | 10篇 |
1970年 | 8篇 |
1968年 | 7篇 |
排序方式: 共有6781条查询结果,搜索用时 15 毫秒
991.
Biology and life history of Dabry's sturgeon, Acipenser dabryanus, in the Yangtze River 总被引:2,自引:0,他引:2
Ping Zhuang Fu'en Ke Qiwei Wei Xuefu He Yuji Cen 《Environmental Biology of Fishes》1997,48(1-4):257-264
Dabry's sturgeon, Acipenser dabryanus, is a relatively small (130 cm, 16 kg) and now rare sturgeon restricted to the Yangtze River Basin. It behaves as a resident freshwater fish, does not undertake long distance migrations (except for spawning), and lives in a variety of habitats. It historically spawned in the upper Yangtze River, but the spawning sites are unknown. Acipenser dabryanus reaches maturity earlier than do other Chinese sturgeons, which gives the species aquaculture potential, and artificial spawning has been carried out. However, the native population in the Yangtze has sharply declined in the last two decades due to overfishing, pollution and habitat alteration and destruction, especially since the construction of the Gezhouba Dam, which was built in 1981 across the Yangtze River at Yichang, Hubei Province. Since 1981, Dabry's sturgeon rarely occurs below the Gezhouba Dam because downstream movements are blocked. Clearly, conservation of Dabry's sturgeon must be emphasized. Conservation methods may include protecting habitats, controlling capture and stock replenishment. 相似文献
992.
从江浙蝮蛇中分离纯化的碱性磷脂酶A2在pH9.5,0.05mmol/LCHES缓冲液中,用汽相悬滴扩散的方法,获得了适用于高分辨率X射线结构分析的单晶.经X200B面探测器分析,表明该晶体属于正交晶系,P2I2I2I空间群,晶胞参数为a=97.13,b=103.69,c=23.27.并收集了一套衍射数据,独立衍射点数12001个,数据完整度为86.2%,Rmerge为0.0459.最高分辨率达2.0,根据分子量与晶胞体积估算,一个不对称单位含两个分子. 相似文献
993.
通过基因枪轰击转化获得转基因小麦植株的研究 总被引:13,自引:1,他引:12
利用JQ-700型高速基因枪将pDM302质粒DNA上的bar基因即PAT酶基因导入了冬小麦品种“农大146”的幼胚中。经过在含有的选择培养基上筛选,得到了9块具有ppt抗性的愈伤组织。PCR电泳检测与PCR-Southern发要交结果显示,外源bar基因已转化进了由其中4块愈伤组织再生出的转基因的小麦植株中。 相似文献
994.
Bernard J Premraj Swaminathan Raja Neel S Bhavesh Ke Shi Ramakrishna V Hosur Muttaiya Sundaralingam Narayanarao Yathindra 《European journal of biochemistry》2004,271(14):2956-2966
The NMR structure of 2',5' d(GGGGCCCC) was determined to gain insights into the structural differences between 2',5'- and 3',5'-linked DNA duplexes that may be relevant in elucidating nature's choice of sugar-phosphate links to encode genetic information. The oligomer assumes a duplex with extended nucleotide repeats formed out of mostly N-type sugar puckers. With the exception of the 5'-terminal guanine that assumes the syn glycosyl conformation, all other bases prefer the anti glycosyl conformation. Base pairs in the duplex exhibit slide (-1.96 A) and intermediate values for X-displacement (-3.23 A), as in ADNA, while their inclination to the helical axis is not prominent. Major and minor grooves display features intermediate to A and BDNA. The duplex structure of iso d(GGGGCCCC) may therefore be best characterized as a hybrid of A and BDNA. Importantly, the results confirm that even 3' deoxy 2',5' DNA supports duplex formation only in the presence of distinct slide (>or=-1.6 A) and X-displacement (>or=-2.5 A) for base pairs, and hence does not favor an ideal BDNA topology characterized by their near-zero values. Such restrictions on base pair movements in 2',5' DNA, which are clearly absent in 3',5' DNA, are expected to impose constraints on its ability for deformability of the kind observed in DNA during its compaction and interaction with proteins. It is therefore conceivable that selection pressure relating to the optimization of topological features might have been a factor in the rejection of 2',5' links in preference to 3',5' links. 相似文献
995.
表皮生长因子受体调控的人鼻咽癌细胞系CNE2分泌蛋白质的筛选 总被引:3,自引:0,他引:3
为筛选表皮生长因子受体(epidermalgrowthfactorreceptor,EGFR)调控的鼻咽癌(nasopharyngealcarcinoma,NPC)细胞的分泌蛋白质,揭示EGFR在NPC发病中的作用机制,采用无血清培养法培养NPC细胞系CNE2,并用转化生长因子(transforminggrowthfactor-α,TGF-α)刺激CNE2细胞24h作为实验组,对照组CNE2细胞不用TGF-α刺激.超滤法脱盐并浓缩两组细胞的培养上清制备分泌蛋白,采用双向凝胶电泳技术(two-dimensionalelectrophoresis,2-DE)分离两组细胞的分泌蛋白,PDquest图像分析软件识别差异表达的蛋白质点,基质辅助激光解吸电离飞行时间质谱(matrix-assistedlaserdesorption/ionizationtimeofflightmassspectrometry,MALDI-TOF-MS)鉴定差异表达蛋白.建立了实验组和对照组CNE2细胞分泌蛋白的2-DE图谱,图像分析识别了22个差异蛋白质点,质谱鉴定了8个非冗余蛋白质,其功能涉及肿瘤细胞侵袭转移、细胞凋亡和增殖,为进一步揭示EGFR在NPC发病中的作用及其机制奠定了基础. 相似文献
996.
997.
998.
999.
Ing. B. Kešner 《International journal of biometeorology》1957,1(1):213-214
Ohne Zusammenfassung 相似文献
1000.
Ke Zhang Ling Mu Ming-Cui Ding Rui Xu Zhao-Jun Ding Jun Liang 《Biochemical and biophysical research communications》2018,495(1):246-253
It has been well documented that changes in ion fluxes across cellular membranes is fundamental in maintaining cellular homeostasis. Dysregulation and/or malfunction of ion channels are critical events in the pathogenesis of diverse diseases, including cancers. In this study, we focused on the study of K+ channels in hepatocellular carcinoma (HCC). By data mining TCGA cohort, the expression of 27 K+ channels was investigated and KCNJ11 was identified as a key dysregulated K+ channels in HCC. KCNJ11 was differentially expressed in HCC and predicted a poor prognosis in HCC patients. Inhibition of NFκB signaling suppressed KCNJ11 expression in HCC cells. Knockdown of KCNJ11 expression inhibited cell proliferation, promoted cell apoptosis, and reduced cell invasive capacity. Mechanistically, we found that KCNJ11 promotes tumor progression through interaction with LDHA and enhancing its enzymatic activity. Pharmacological inhibition of LDHA largely compromised the oncogenic function of KCNJ11 in cell proliferation, cell apoptosis, and cell invasion. Collectively, our data, as a proof of principle, demonstrate that KCNJ11 acts as an oncogene in HCC though forming a complex with LDHA and suggest that targeting KCNJ11 can be developed as a candidate tool to dampen HCC. 相似文献