全文获取类型
收费全文 | 19489篇 |
免费 | 2045篇 |
国内免费 | 2734篇 |
出版年
2024年 | 36篇 |
2023年 | 280篇 |
2022年 | 534篇 |
2021年 | 921篇 |
2020年 | 674篇 |
2019年 | 930篇 |
2018年 | 865篇 |
2017年 | 707篇 |
2016年 | 886篇 |
2015年 | 1267篇 |
2014年 | 1479篇 |
2013年 | 1542篇 |
2012年 | 1871篇 |
2011年 | 1719篇 |
2010年 | 1140篇 |
2009年 | 1053篇 |
2008年 | 1202篇 |
2007年 | 1035篇 |
2006年 | 948篇 |
2005年 | 844篇 |
2004年 | 749篇 |
2003年 | 677篇 |
2002年 | 617篇 |
2001年 | 415篇 |
2000年 | 323篇 |
1999年 | 283篇 |
1998年 | 179篇 |
1997年 | 147篇 |
1996年 | 109篇 |
1995年 | 70篇 |
1994年 | 84篇 |
1993年 | 49篇 |
1992年 | 80篇 |
1991年 | 63篇 |
1990年 | 69篇 |
1989年 | 47篇 |
1988年 | 36篇 |
1987年 | 30篇 |
1986年 | 43篇 |
1985年 | 30篇 |
1984年 | 20篇 |
1983年 | 28篇 |
1982年 | 15篇 |
1981年 | 17篇 |
1979年 | 23篇 |
1978年 | 13篇 |
1977年 | 15篇 |
1976年 | 14篇 |
1975年 | 15篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
K Y Hui J A Jakubowski V L Wyss E L Angleton 《Biochemical and biophysical research communications》1992,184(2):790-796
A site-specific proteolytically generated neoamino terminus of the thrombin receptor having a sequence SFLLRNPNDKYEPF- has been reported to be a functional ligand of the receptor. This discovery raises question on the precise structural requirements of the "tethered ligand" responsible for receptor activation and signal transduction. By examining the agonist activity of a panel of synthetic sequence analogues of thrombin receptor agonist peptides (TRAP) on human platelet aggregation, we determined that the minimal sequence of the human platelet thrombin receptor ligand is SFLL-amide (TRAP1-4, EC50 = 300 uM). An extension of TRAP1-4 by an additional Arg-Asn segment yielded the most potent agonist among the series (TRAP1-6, EC50 = 1.3 microM). Based on the structure-activity relationships, we hypothesized a model of the ligand-binding site of the human platelet thrombin receptor that accommodates a hexapeptide structure. TRAP1-6, when administered intravenously, induced marked intravascular platelet aggregation in the anesthetized guinea pigs. 相似文献
72.
将乙酰胆碱(ACh)注入麻醉家兔脊髓蛛网膜下腔,观察其对心血管活动的影响。结果表明:(1)脊髓蛛网膜下腔注射50~100μg ACh可使血压下降,心率减慢;(2)预先由脊髓蛛网膜下腔注射阿托品,可阻断ACh引起的降压和降心率作用;(3)脊髓蛛网膜下腔注射六甲双铵、酚妥拉明或心得安均不能阻断上述ACh的心血管反应;(4)切断两侧颈部迷走神经,ACh不再使心率减慢,但其降低血压的作用不受到任何影响。 脊髓中ACh水平升高可通过激活胆碱能M-受体引起血压下降和心率减慢。ACh的这种降压作用既没有中枢肾上腺素能受体活动参与,也不是通过迷走神经实现的,可能是由于脊髓交感血管中枢紧张性降低所造成的。 相似文献
73.
Genetic Interactions between Reg1/Hex2 and Glc7, the Gene Encoding the Protein Phosphatase Type 1 Catalytic Subunit in Saccharomyces Cerevisiae 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Mutations in GLC7, the gene encoding the type 1 protein phosphatase catalytic subunit, cause a variety of abberrant phenotypes in yeast, such as impaired glycogen synthesis and relief of glucose repression of the expression of some genes. Loss of function of the REG1/HEX2 gene, necessary for glucose repression of several genes, was found to suppress the glycogen-deficient phenotype of the glc7-1 allele. Deletion of REG1 in a wild-type background led to overaccumulation of glycogen as well as slow growth and an enlarged cell size. However, loss of REG1 did not suppress other phenotypes associated with GLC7 mutations, such as inability to sporulate or, in cells bearing the glc7(Y-170) allele, lack of growth at 14°. The effect of REG1 deletion on glycogen accumulation is not simply due to derepression of glucose-repressed genes, although it does require the presence of SNF1, which encodes a protein kinase essential for expression of glucose-repressed genes and for glycogen accumulation. We propose that REG1 has a role in controlling glycogen accumulation. 相似文献
74.
小麦×玉米杂交后代的蛋白质及酯酶同工酶分析 总被引:9,自引:0,他引:9
以8 个普通小麦(Triticum aestivum L.)品种为母本,2 个栽培玉米(Zea m ays L.)品种为父本杂交所获得的F2 代在形态上出现了明显变异。对其籽粒进行蛋白质电泳分析,得到了如下主要结果:杂交后代的蛋白质谱带较母本有了很大的变异,主要集中在高分子量麦谷蛋白(HMW-Glu)区域。杂交后代的蛋白质谱带由5 种类型构成:1.母本型,占全部测试籽粒的22.6% ;2.附加型,占14.3% ;3.互补型,占15.5% ;4.杂种型,占30.9% ;5.缺失型,占16.7% 。对“矮杆早”ד紫粘”的F2 代籽粒进行酯酶同工酶电泳分析发现,变异主要发生在EST-1 区。由此看来,小麦×玉米的杂合子中玉米染色体在被排除前后,可以诱发小麦染色体组发生遗传变异 相似文献
75.
John O. Hui John Le Viswanatham Katta Robert Rosenfeld Michael F. Rohde Mitsuru Haniu 《Journal of Protein Chemistry》1996,15(4):351-358
Human neurotrophin-3 (NT-3) is a member of the nerve growth factor (NGF) family of neurotrophic factors, and the recombinant protein is being developed as a therapeutic for neurodegenerative diseases. The final product purity and lot-to-lot variation are monitored routinely by peptide mapping. However, only the N-terminal region of NT-3 was susceptible to proteolysis under native conditions. Complete digestion required that the protein be chemically modified by reduction and S-alkylation prior to proteolysis. Complete proteolytic degradation of the protein was achieved simply by an intial denaturation of NT-3 in 6 M guanidinium chloride (pH 6) for 2 hr at 37°C, followed by a tenfold dilution with the digestion buffer (0.1 M Tris-HCl, 1 mM CaCl2 at pH 7.0) and immediate addition of chymotrypsin at 1% by weight. Direct comparison of the peptide map with an identical aliquot that had been reduced and alkylated also allowed the establishment of the cystine linkages present in NT-3: Cys14 to Cys79, Cys57 to Cys108, and Cys67 to Cys110. This disulfide structure is homologous to the NGF family of neurotrophic factors. 相似文献
76.
In the search for candidate genes for the tuberous sclerosis (TSC1) disease locus on chromosome 9q34, we have isolated an overlapping series of 22 plasmid and phage cDNA clones covering nearly 7 kb and with an open reading frame of 5070 bp encoding a protein of 1690 amino acids. The putative protein product is a member of the kinesin superfamily and is homologous to the mouse KIF1A and theCaenorhabditas elegansunc-104 genes. Both KIF1A and unc-104 function in the anterograde axonal transport of synaptic vesicles. The human homolog is therefore termed H-ATSV (axonal transporter of synaptic vesicles, HGMW-approved nomenclature ATSV) Screening of DNA from 107 tuberous sclerosis patients and 80 unaffected individuals with H-ATSV cDNA probes by pulsed-field gel electrophoresis/Southern blotting following digestion by rare-cutting methylation-sensitive restriction enzymes showed variant banding patterns in three patients with tuberous sclerosis. However, further analysis indicated that these variant fragments represent a rare polymorphism probably associated with methylation of clustered restriction sites. There is no evidence to support H-ATSV as a candidate gene for TSC1. 相似文献
77.
二核苷酸重复多态性的非同位素检测及其在基因诊断中的应用 总被引:9,自引:1,他引:8
本文报道了一种检测二核苷酸重复多态性的简便的非同位素法,利用重复序列两侧的特异引物进行PCR扩增,产生的等位片段在薄层变性聚丙烯酰胺凝胶电泳上分离,再用灵敏的银染法显色。该方法不需要标记PCR产物,简便、快速,分辨率可达1bp,并可用多对引物同时进行多重PCR分析。用此方法对DMD家系成员dystrophin基因的5'-脑型外显子止游区和3'-非翻译区的两个(CA)。位点进行了扩增片段长度多态性分 相似文献
78.
用蛋白质工程方法改变葡萄糖异构酶最适pH和最适温度 总被引:5,自引:2,他引:3
用寡核苷酸诱导的定点突变方法构建了葡萄糖异构酶基因的突变体(N184D和A198C)。含突变体的重组质粒pTKD-GI1(N184D)和pTKD-GI2(A198c)在E.coliK38菌株中表达,用DEAE-Sepharose FF和Sephacryl S-300HR柱层析分离纯化突变酶。与野生型葡萄糖异构酶比较实验表明:(1)突变酶N184D的最适pH值下降了1个单位;等电点下降了0.6个单位 相似文献
79.
利用PCR方法对单纯疱疹病毒Ⅱ型糖蛋白D(HSV-2gD)基因进行了修饰,在其5'端删去约500bp的非编码区,仅保留ATG上游7个bp。将修饰后的HSV-2gD基因插入到带有痘苗病毒天坛株TK基因区段的痘苗表达质粒pJSA1175,置于痘苗病毒P7.5k早/晚期启动子控制下。将此重组质粒用脂质体Lipofectin方法转染已受野型TK ̄+痘苗病毒天坛株感染的TK ̄-143细胞,通过同源重组机制和标志基因LacZ产物的蓝斑显色作用,以及BudR试剂对TK表型的选择压力,筛选出整合有HSV-2gD基因的重组痘苗病毒。Southem杂交表明,HSV-2gD基因已正确地插入痘苗病毒TK基因区内;间接免疫荧光检测显示,HSV-2gD蛋白已得到有效表达,且主要分布于细胞膜。重组病毒免疫家兔可产生明显的抗HSV-2gD中和抗体。用重组病毒免疫小鼠,3周后可使94%(17/18)的小鼠对抗HSV-2的致死量攻击,表明重组病毒具有明显的免疫保护作用。 相似文献
80.
酪氨酸羟化酶基因载体-pCMVTH 质粒的构建及在大鼠骨骼肌内的表达 总被引:4,自引:0,他引:4
为用转基因方法治疗巴金森氏病大鼠模型,本研究采用分子克隆技术,将合成多巴胺的关键酶-酪氨酸羟化酶(TH)的基因,克隆进入以巨细胞病毒CMV为启动子的载体质粒内,经限制性内切酶定位分析证实该重组的DNA质粒的可靠性。携带TH基因的PCMVTH质粒以LIPO-FECTIN介导,在培养的原代骨骼肌细胞中高效表达。本研究为进一步用转基因的细胞植入脑内以治疗巴金森氏病打下一定基础。 相似文献