全文获取类型
收费全文 | 101283篇 |
免费 | 6465篇 |
国内免费 | 12篇 |
出版年
2023年 | 642篇 |
2022年 | 768篇 |
2021年 | 1605篇 |
2020年 | 1283篇 |
2019年 | 1486篇 |
2018年 | 2956篇 |
2017年 | 2642篇 |
2016年 | 3595篇 |
2015年 | 4636篇 |
2014年 | 4811篇 |
2013年 | 6515篇 |
2012年 | 7526篇 |
2011年 | 6889篇 |
2010年 | 4428篇 |
2009年 | 3503篇 |
2008年 | 5283篇 |
2007年 | 5049篇 |
2006年 | 4914篇 |
2005年 | 4146篇 |
2004年 | 4057篇 |
2003年 | 3663篇 |
2002年 | 3392篇 |
2001年 | 2365篇 |
2000年 | 2317篇 |
1999年 | 1813篇 |
1998年 | 864篇 |
1997年 | 617篇 |
1996年 | 611篇 |
1995年 | 593篇 |
1994年 | 461篇 |
1993年 | 426篇 |
1992年 | 1005篇 |
1991年 | 875篇 |
1990年 | 803篇 |
1989年 | 799篇 |
1988年 | 733篇 |
1987年 | 711篇 |
1986年 | 644篇 |
1985年 | 632篇 |
1984年 | 598篇 |
1983年 | 453篇 |
1982年 | 409篇 |
1979年 | 491篇 |
1978年 | 381篇 |
1975年 | 356篇 |
1974年 | 410篇 |
1973年 | 408篇 |
1972年 | 364篇 |
1970年 | 347篇 |
1969年 | 343篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
951.
In contrast to the inhibition by gentamicin of glucose production from propionate, pyruvate and lactate in renal tubules incubated at 2.5 mM Ca2+, this antibiotic does not affect gluconeogenesis from propionate and lactate, and significantly stimulates this process from other substrates at 0.5 mM Ca2+. This may be due to the gentamicin-induced increase of the cytosolic manganese content (from 1.7 to 2.7 nmol/mg protein), resulting in a stimulation of cytosolic phosphoenolpyruvate carboxykinase activity. At 2.5 mM Ca2+ the cytosolic Mn content (2.7 nmol/mg protein) seems to be high enough to accomplish activation of the enzyme. 相似文献
952.
Penetration of intact bovine ova with ram sperm in vitro 总被引:1,自引:0,他引:1
In culture, mature bovine ovarian oocytes were fertilized in vitro with freshly ejaculated ram spermatozoa treated with heparin. The zona pellucida does not prevent penetration of ram spermatozoa. The penetration rate varied between 10 and 84%, and in most instances, after 24 hr of culture, two normal-looking pronuclei and sperm tail were present in the cytoplasm. These results suggest that the zona pellucida of bovine oocytes does not represent a barrier for the penetration of ram spermatozoa. 相似文献
953.
Argyrophilic nuclear proteins, known to be functionally associated with ribosomal genes, were localized, in four-, eight-, and 16-cell bovine embryo blastomere nuclei using two different silver-staining procedures. Within the eight-cell cleavage stage by the process of embryonal nucleologenesis in the cow embryo the full-capacity ribosome-producing machinery is established. In the four-cell embryo, many patches and islands of argyrophilic (Ag+) material were detected in the nucleoplasm. The nucleolus-precursor bodies (NPBs), composed uniformly of a homogeneous compact mass, were completely devoid of any silver staining. On the other hand, clear-cut localization of argyrophilic proteins was detected during the eight-cell stage either inside the transforming NPBs or in the close vicinity, or in the already differentiated nucleolus. In compact, nonvacuolated NPB, an intensive Ag+ area was detected, in the form of a lenticle, at the periphery of the NPB. During and following vacuolation of the NPB, no Ag+ was detected inside these vacuoles. It was seen, however, in the dense fibrillar nucleolar component surrounding the smaller vacuoles formed at the time of the establishment of nucleolar structure. Ag+ areas were seen repeatedly in the vicinity of NPBs, probably a part of the nucleolus-associated chromatin or, alternatively, representing the extranucleolar bodies. In blastomere nuclei of 16-cell embryos, already possessing reticulated nucleoli known from intensively synthesizing somatic cells, the silver-staining pattern corresponded to the usual situation in differentiated cells: slight staining of fibrillar centers, heavy labelling in the dense fibrillar component, and absence of silver deposits in the granular component.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
954.
955.
956.
K. Thórarinsson 《BioControl》1990,35(1):107-118
Measurements of body length of cottony-cushion scales,Icerya purchasi Maskell, are presented. Although length increased markedly with developmental stage, the length distributions of successive
stages were found to overlap, making length an imperfect indicator of stage andvice versa. The likelihood of parasitism by the fly,Cryptochaetum iceryae (Williston), was found to increase with increasing scale size when scales of different sizes were concurrently made available
to the parasites under field conditions. Also, parasite loads (no. of parasites per parasitized host) were found to increase
with host size. The size ofC. iceryae pupae was found to depend on the developmental stage of the scale host in which pupation took place — the more developed
(larger) the host, the larger the pupa. This result suggests that parasite growth is food limited in the smaller hosts, and
that therefore its apparent preference for larger hosts is to the parasite's advantage.
相似文献
957.
958.
959.
960.
M. Torras-Llort R. Ferrer J.F. Soriano-García M. Moretó 《The Journal of membrane biology》1996,152(3):183-193
The properties of l-lysine transport in chicken jejunum have been studied in brush border membrane vesicles isolated from 6-wk-old birds. l-lysine uptake was found to occur within an osmotically active space with significant binding to the membrane. The vesicles
can accumulate l-lysine against a concentration gradient, by a membrane potential-sensitive mechanism. The kinetics of l-lysine transport were described by two saturable processes: first, a high affinity-transport system (K
mA= 2.4 ± 0.7 μmol/L) which recognizes cationic and also neutral amino acids with similar affinity in the presence or absence
of Na+ (l-methionine inhibition constant KiA, NaSCN = 21.0 ± 8.7 μmol/L and KSCN = 55.0 ± 8.4 μmol/L); second, a low-affinity transport mechanism (KmB= 164.0 ± 13.0 μmol/L) which also recognizes neutral amino acids. This latter system shows a higher affinity in the presence
of Na+ (KiB for l-methionine, NaSCN = 1.7 ± 0.3 and KSCN = 3.4 ± 0.9 mmol/L). l-lysine influx was significantly reduced with N-ethylmaleimide (0.5 mmol/L) treatment. Accelerative exchange of extravesicular labeled l-lysine was demonstrated in vesicles preloaded with 1 mmol/L l-lysine, l-arginine or l-methionine. Results support the view that l-lysine is transported in the chicken jejunum by two transport systems, A and B, with properties similar to those described
for systems b
0,+ and y+, respectively.
Received: 14 August 1995/Revised: 2 April 1996 相似文献