全文获取类型
收费全文 | 8331篇 |
免费 | 623篇 |
国内免费 | 7篇 |
专业分类
8961篇 |
出版年
2023年 | 51篇 |
2022年 | 127篇 |
2021年 | 210篇 |
2020年 | 108篇 |
2019年 | 122篇 |
2018年 | 164篇 |
2017年 | 149篇 |
2016年 | 226篇 |
2015年 | 362篇 |
2014年 | 344篇 |
2013年 | 495篇 |
2012年 | 610篇 |
2011年 | 520篇 |
2010年 | 353篇 |
2009年 | 279篇 |
2008年 | 424篇 |
2007年 | 427篇 |
2006年 | 378篇 |
2005年 | 334篇 |
2004年 | 312篇 |
2003年 | 262篇 |
2002年 | 244篇 |
2001年 | 228篇 |
2000年 | 191篇 |
1999年 | 159篇 |
1998年 | 66篇 |
1997年 | 62篇 |
1996年 | 36篇 |
1995年 | 53篇 |
1994年 | 46篇 |
1993年 | 40篇 |
1992年 | 111篇 |
1991年 | 101篇 |
1990年 | 103篇 |
1989年 | 101篇 |
1988年 | 79篇 |
1987年 | 77篇 |
1986年 | 90篇 |
1985年 | 88篇 |
1984年 | 80篇 |
1983年 | 70篇 |
1982年 | 59篇 |
1981年 | 41篇 |
1980年 | 43篇 |
1979年 | 57篇 |
1978年 | 39篇 |
1976年 | 41篇 |
1975年 | 41篇 |
1974年 | 46篇 |
1973年 | 44篇 |
排序方式: 共有8961条查询结果,搜索用时 15 毫秒
161.
1H-NMR study of the lambda operator site OL1: assignment of the imino and adenine H2 resonances. 总被引:4,自引:3,他引:1
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
One- and two-dimensional proton NMR methods are being used to study the synthetic lambda operator site O-L1, a 17 base-pair DNA duplex recognized by lambda repressor and Cro protein. The complete assignment of the 17 imino protons, which participate in Watson-Crick hydrogen bonding, and of the eight adenine H2 protons, which lie in the minor groove of the double helix, is presented. 相似文献
162.
Summary The localisation of tyrosine-hydroxylase immunoreactive neurones in retinas of a variety of animals were examined. Immunoreactivity was associated with specific populations of amacrine neurones in all species examined, viz; rabbit, guinea pig, monkey, cow, frog, pigeon and goldfish. Only in the goldfish was immunoreactivity also associated with processes situated in the outer plexiform layer showing that in this species catecholamine interplexiform cells exist.The development of tyrosine-hydroxylase immunoreactive neurones in the rabbit retina was also analysed. The first immunoreactive positive cells were observed by the third postnatal day. The immunoreactive positive neurones at this stage are weak and lack processes. The intensity of the immunoreactivity increases with development, but processes are lacking, until the 10th postnatal day. The immunoreactive neurones only appear fully developed by the 22nd to 28th postnatal day.Autoradiographical analysis of 3H-dopamine uptake strongly suggests that neurones containing tyrosine-hydroxylase immunoreactivity in the different retinas have the capacity to take up exogenous dopamine. It is therefore concluded that localisation of either 3H-dopamine uptake or tyrosine-hydroxylase provides a means of locating catecholamine neurones. 相似文献
163.
Prolific shoot bud differentiation was induced in callus and suspension cultures of hypocotyl origin in Brassica campestris cv. Yellow Sarson on MS medium supplemented with K (13.9–23.2 M) or BA (13.3–22.1 M). Plantlets were obtained by rooting the in vitro differentiated shoots. Histological studies revealed a unique mode of meristemoid formation.Abbreviations MS
Murashige and Skoog (1962)
- 2,4-D
2,4-dichlorophenoxyacetic acid
- BA
Benzyladenine
- IAA
Indole-3-acetic acid
- IBA
Indolebutyric acid
- K
Kinetin
- NAA
Naphthalene acetic acid 相似文献
164.
A panel of monoclonal antibodies and conventional antisera directed against desmosomal proteins from bovine muzzle epidermis was used to identify immunologically related proteins from two other bovine stratified squamous epithelia, cornea and esophagus. Desmosome-enriched tissue fractions were prepared from epidermis, cornea, and esophagus. These tissue extracts were electrophoresed on sodium dodecyl sulfate (SDS)-polyacrylamide gels, blotted onto nitrocellulose paper, and labeled using an indirect immunoperoxidase technique. Labeling with the conventional antisera demonstrates that each of the previously characterized epidermal desmosomal proteins or protein families has an immunologically cross-reacting counterpart in cornea and esophagus. However, chemical differences between homologous desmosomal proteins in these three tissues have also been detected. The corresponding proteins in the different tissues have similar but not always identical apparent molecular weights. Moreover, tissue-restricted antigenic determinants were detected in two of the desmosomal proteins families using four monoclonal antibodies, each of which recognizes a distinct antigenic determinant. 相似文献
165.
K R Patel 《BMJ (Clinical research ed.)》1984,288(6429):1496-1497
166.
167.
Presence of Epstein-Barr virus receptors, but absence of virus penetration, in cells of an Epstein-Barr virus genome-negative human lymphoblastoid T line (Molt 4). 总被引:5,自引:0,他引:5
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper reports a unique type of interaction of Epstein-Barr virus (EBV) with an EBV receptor-positive, genome-negative human lymphoid T cell line (Molt 4), which can be summarized as follows. Although Molt 4 cells express receptors for EBV, they appear to block the penetration of this virus. These observations are derived from combined studies with immunofluorescence and electron microscopy. It is possible that T cell lines bearing receptors for EBV may express such a control on virus penetration. 相似文献
168.
Using liposomes differing in size and lipid composition, we have studied the uptake characteristics of the liver parenchymal and Kupffer cells. Desferal labeled with iron-59 was chosen as a radiomarker for the liposomal content, because Desferal in its free form does not cross cellular membranes. At various time intervals after an intravenous injection of liposomes into mice, the liver was perfused with collagenase, and the cells were separated in a Percoll gradient. It was found that large multilamellar liposomes (diameter of about 0.5 μm) were mainly taken up by the Kupffer cells. For these large liposomes, the rate of uptake by Kupffer cells was rapid, with maximum uptake at around 2 hours after liposome injection. Unexpectedly, small unilamellar liposomes (diameter of about 0.08 μm) were less effectively taken up by Kupffer cells, and the rate of uptake was slow, with a maximum uptake at about 10 hours after liposome injection. In contrast, parenchymal cells were more effective in taking up small liposomes and the uptake of large liposomes was negligible. In addition, liposomes made with a galactolipid as part of the lipid constituents appeared to have higher affinity to parenchymal cells than liposomes made without the galactolipid. These findings should be of importance in designing suitable liposomes for drug targeting. 相似文献
169.
This report concerns the isolation of bullous pemphigoid antigen from the nondialyzable urinary components of a patient with the disease. The isolation was accomplished by ion exchange chromatography and gel filtration. Pemphigoid antigen was found to be a basic glycoprotein that on SDS gel electrophoresis showed two major bands, one in the 18,000 m. w. region and the second with a m. w. of 74,000. Between these two bands, two additional bands appeared; one of 35,000 daltons and the other of 68,000 daltons. The 18,000 m. w. band was eluted from the gel and rerun on SDS gels. These gels showed the 18,000 m.w. band and also the appearance of the 35,000 and 74,000 m.w. bands. This finding indicates that urinary pemphigoid antigen may exist both as a single monomeric form and in polymeric aggregates. 相似文献
170.
A high-yield synthesis of saturated, unsaturated, and short chain phosphatidylcholines from sn-glycero-3-phosphocholine is described. The procedure offers advantages over other reported procedures for the synthesis of phosphatidylcholine in that the large-scale synthesis and purification can be achieved in a minimum time. The procedure utilizes 4-pyrrolidinopyridine as a catalyst and moderate amounts of fatty acid anhydride (2 mol eq. of fatty acid anhydride per mol of OH) in a 1:1 mixture of benzene-dimethylsulfoxide (DMSO) at 40 degrees--42 degrees C (oilbath) for 2--5 hr. At the end of the reaction, the phosphatidylcholine can be purified in the usual manner or by using a Waters Prep LC/500 with a radially compressed silica gel column eluted with chloroform-methanol-water 60:30:4. At a flow rate of 200 ml/min, the phospholipid elutes in 10--15 min, depending on the chain length and unsaturation. 相似文献