全文获取类型
收费全文 | 25276篇 |
免费 | 2193篇 |
国内免费 | 2297篇 |
出版年
2024年 | 33篇 |
2023年 | 194篇 |
2022年 | 434篇 |
2021年 | 756篇 |
2020年 | 648篇 |
2019年 | 755篇 |
2018年 | 772篇 |
2017年 | 659篇 |
2016年 | 895篇 |
2015年 | 1452篇 |
2014年 | 1653篇 |
2013年 | 1839篇 |
2012年 | 2316篇 |
2011年 | 1986篇 |
2010年 | 1432篇 |
2009年 | 1275篇 |
2008年 | 1609篇 |
2007年 | 1466篇 |
2006年 | 1381篇 |
2005年 | 1278篇 |
2004年 | 1175篇 |
2003年 | 1043篇 |
2002年 | 883篇 |
2001年 | 579篇 |
2000年 | 490篇 |
1999年 | 450篇 |
1998年 | 296篇 |
1997年 | 229篇 |
1996年 | 202篇 |
1995年 | 183篇 |
1994年 | 158篇 |
1993年 | 121篇 |
1992年 | 153篇 |
1991年 | 124篇 |
1990年 | 100篇 |
1989年 | 100篇 |
1988年 | 71篇 |
1987年 | 82篇 |
1986年 | 65篇 |
1985年 | 39篇 |
1984年 | 28篇 |
1983年 | 44篇 |
1982年 | 20篇 |
1981年 | 26篇 |
1979年 | 22篇 |
1978年 | 19篇 |
1977年 | 20篇 |
1976年 | 18篇 |
1970年 | 20篇 |
1969年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Gwang Hoon Gil Seung Rim Kim Jong Chan Bae Jae Heung Lee 《Enzyme and microbial technology》1985,7(8):370-372
Effects of inoculum size and total sugar content on both l-phenylalanine productivity and titre have been investigated using a tyrosine auxotrophic regulatory mutant of Escherichia coli. Fermentations were carried out in a 500 litre pilot fermenter with intermittent feeding of d-glucose plus phosphate. It was found that the productivity was not greatly affected by inoculum size. However, the l-phenylalanine titre was significantly affected by total sugar content. Relatively high productivities of up to 0.35–0.40 g l-phenylalanine l?1 h?1 have been achieved at l-phenylalanine titres of 14–15 g l?1. 相似文献
82.
Formation of protoplasts and their reversion were followed in 7 strains of brevibacteria. The formation of protoplasts and
their reversion differed both between various species of brevibacteria and between various mutant strains of the same species. 相似文献
83.
84.
甜菊不同叶龄细胞结构及其甜菊糖甙含量分布的研究 总被引:2,自引:0,他引:2
洪维廉;陈睦传;李里焜;刘丹 《武汉植物学研究》1987,5(3):211-218
本文报道甜菊(Stevia rebaudiana Bertoni)不同叶龄细胞结构与甜菊糖苷含量分布。应用电镜技术观察表明,现蕾期成叶细胞内具有内含物丰富的巨大液泡,这些内含物呈大小不一的颗粒或小泡。应用差速离心法,对甜菊成叶的叶肉细胞进行亚细胞分离,并对各部分进行甜菊糖苷的提取与微量测定。结果表明,甜菊糖苷主要存在于12000g的上清液(这部分主要包括液泡内含物和可溶性细胞质)。结合细胞结构和细胞化学研究结果,表明细胞质是合成UDPG的主要场所,在甜菊糖苷合成中具有重要作用。对不同叶龄叶片甜菊糖苷测定表明,现蕾期成叶的甜菊糖苷含量最高。从甜菊不同叶龄细胞结构和甜菊糖苷含量测定结果,现蕾期是甜菊叶片收割的最适时期。 相似文献
85.
油松茎次生结构中树脂道的结构分布和发育的研究 总被引:6,自引:0,他引:6
油松茎的次生结构中树脂道存在于次生维管组织中。其中,次生木质部内具有水平的和垂直的两类树脂道,而次生韧皮部内则仅有水平的树脂道。两类树脂道都由上皮细胞和鞘细胞包围着胞间道构成,其中木质部内的树脂道具有死鞘细胞,而韧皮部中的则都系生活细胞。在心材中,垂直树脂道形成拟侵填体。在次生木质部内,垂直树脂道常分布于早材的外部区域和最初形成的晚材中,它们与水平树脂道连接,腔道贯通,从而形成二维网状结构。垂直树脂道来源于纺锤状原始细胞的衍生细胞,而水平树脂道来源于射线原始细胞,两者都以裂生方式发生。 相似文献
86.
用淀粉胶电泳及特异染色的方法,对我国9个民族的腺苷酸激酶(AK)多态分布进行了测定。9个民族中维吾尔族AK表型分布具有多态性。维吾尔族中AK_1~1基因频率为0.965,AK_1~2基因频率为0.035,而侗、回、白、土家、苗、彝、藏、满等8个民族的AK_1~2均未达到多态水平。在9个民族中AK_1表型分布均符合Hardy-Weinberg平衡,并且未发现其它罕见表型。 相似文献
87.
Mating behaviour ofTokunagayusurika akamusi searching at the resting place (lakeside vegetation, although mating also occurs in the air by swarming) was investigated
at the shore of Lake Biwa. Coinciding with the arrival of newly emerged adults, previously emerged males walked about to search
for mates at the resting place. When a searching male came into contact with a fresh (newly emerged) individual, he attempted
to copulate with it regardless of its sex. Consequently, males copulated with fresh females, which were more likely to be
virgin at the resting place, suggesting that the first male might contribute best to the fertilization. 相似文献
88.
Observations on the mating system of the midge,Tokunagayusurika akamusi, revealed mating to occur both in the air by swarming and on the ground by searching. At the shores of Lake Biwa, midges
appeared from November to early December. Newly emerged adults arrived at the resting place, lakeside vegetation, in the morning,
during which time a number of males also walked about in search of mates. Many copulating pairs were observed at the resting
place. Huge swarms occurred chiefly before sunset but the frequency of copulation observed in the swarm was extremely low.
It is likely that, in the Lake Biwa population, the proportion of females inseminated by searching males at the resting place
was much larger than that by swarming males in the air. Furthermore, by searching, males copulated with younger females than
by swarming. The differences between the searching and swarming tactics are discussed. 相似文献
89.
György Vereb Konélia Szücs Judit Szabó Magdaléna Belanova György Bot 《Molecular and cellular biochemistry》1986,69(2):139-146
Summary Phosphorylase ab hybrid was demonstrated in perfused rat hearts and during the in vitro conversion of purified rat heart phosphorylase b. Phosphorylase ab hybrid was determined in rat heart extracts by the activating effect of AMP in the presence of caffeine. These results were confirmed by the quantitative determination of incorporated 32P in vitro and through the characteristic inhibition of ab hybrid by glucose-6-phosphate.As shown by our results, in aerobically perfused control hearts only the ab hybrid represents the active form of phosphorylase, its activity reaching about 20% of the total. In response to isoproterenol (5–1000 ng), the amount of ab hybrid rose to about 30–40%, preceding the rise of the a form, which increased in a dose-dependent manner up to 45% of the total.The great sensitivity of the ab form to AMP activation and glucose-6-phosphate inhibition supports its physiological significance in heart under in vivo conditions as well. Our results strongly suggest that the activity ratio -AMP/+AMP reflects rather the percentage ratio of phosphorylated subunits than that of the activated (partially or totally phosphorylated) phosphorylase molecules. 相似文献
90.
A S Abramovitz J Y Hong V Randolph 《Biochemical and biophysical research communications》1983,117(1):22-29
We have previously reported the purification of polypeptides from soybean which are potent inhibitors of superoxide production by human neutrophils. We now report that neither oxygen uptake nor hydrogen peroxide production by stimulated neutrophils is affected by these inhibitors. Furthermore, the E-1 and E-3 polypeptides inhibit ferricytochrome c reduction by a xanthine oxidase superoxide generation system. The inhibitory activity of E-3 in the model system is blocked by 1 mM KCN while E-1 is only slightly cyanide sensitive. Atomic absorption analysis of E-1 and E-3 polypeptides reveal copper in the latter and manganese in the former. Thus, E-3 is a copper-containing superoxide dismutase while E-1 appears to be a manganese-containing superoxide dismutase. 相似文献