全文获取类型
收费全文 | 44075篇 |
免费 | 16467篇 |
国内免费 | 13篇 |
出版年
2023年 | 61篇 |
2022年 | 307篇 |
2021年 | 751篇 |
2020年 | 2332篇 |
2019年 | 3900篇 |
2018年 | 4128篇 |
2017年 | 4373篇 |
2016年 | 4585篇 |
2015年 | 4867篇 |
2014年 | 4649篇 |
2013年 | 5181篇 |
2012年 | 3320篇 |
2011年 | 2951篇 |
2010年 | 3893篇 |
2009年 | 2562篇 |
2008年 | 1806篇 |
2007年 | 1391篇 |
2006年 | 1247篇 |
2005年 | 1221篇 |
2004年 | 1147篇 |
2003年 | 1018篇 |
2002年 | 919篇 |
2001年 | 805篇 |
2000年 | 660篇 |
1999年 | 512篇 |
1998年 | 162篇 |
1997年 | 153篇 |
1996年 | 102篇 |
1995年 | 110篇 |
1994年 | 70篇 |
1993年 | 61篇 |
1992年 | 127篇 |
1991年 | 140篇 |
1990年 | 91篇 |
1989年 | 109篇 |
1988年 | 88篇 |
1987年 | 70篇 |
1986年 | 61篇 |
1985年 | 74篇 |
1984年 | 59篇 |
1983年 | 35篇 |
1982年 | 28篇 |
1979年 | 30篇 |
1978年 | 35篇 |
1977年 | 33篇 |
1976年 | 31篇 |
1974年 | 36篇 |
1973年 | 33篇 |
1972年 | 26篇 |
1971年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Status of metacercarial infections of Paragonimus westermani was observed in freshwater crabs, which were purchased at 3 markets in its peak season of 1990. All of 85 crabs were Eriocheir japonicus. No other species of Eriocheir were found. When crushed muscle and viscera was examined individually, the infection rate was 11.8%; and mean number of metacercariae was 2.1 per infected crab. Unless adequately cooked, freshwater crabs are still potential sources of human paragonimiasis. 相似文献
172.
A case of anisakiasis causing intestinal obstruction 总被引:1,自引:0,他引:1
A 31-year old salesman living in Seoul developed suddenly abdominal pain due to intestinal obstruction. Exploratory laparotomy exhibited segmental jejunal cellulitis caused by penetrating Anisakis larva. The patient had eaten raw fish. The typical history of intestinal anisakiasis was presented with a short review of Korean patients of anisakiasis. 相似文献
173.
The nature of 2 component proteins in crude saline extract of adult Paragonimus westermani was investigated. By immunoaffinity chromatography using monoclonal antibodies (MAb) as ligands, the proteins were purified from the crude extract. Band 1 protein in disc-polyacrylamide gel electrophoresis (PAGE) was purified by PFCK-136 MAb. The protein, known to have molecular mass of 440 kDa, was composed of 23, 46 and 92 kDa subunits when observed by reducing SDS-PAGE and SDS-PAGE/immunoblot. This protein was originated from eggs of the worm as revealed by immunohistochemical staining with PFCK-136 Mab. Another affinity purified protein utilizing PFCK-44 MAb was the band 4 protein of 17 kDa in disc-PAGE. This was a monomer protein in reducing SDS-PAGE and SDS-PAGE/immunoblot. The protein was produced at intestinal epithelium of the worm. 相似文献
174.
In order to determine the vector species of tsutsugamushi disease in Korea, chiggers were individually dissected, and internal contents were tested for Rickettsia tsutsugamushi organisms by means of indirect FA test, and each exoskeleton was mounted on slide for identification. Among 4,142 chiggers collected from 48 Apodemus agrarius at nine different localities during the period of July-November, 1989, 990 chiggers of 10 species of Trombiculidae were dissected and tested. Rickettsiae were confirmed in two Leptotrombidium pallidum larvae out of 447 tested, giving 0.4% of the infection rate. The chiggers of the other species tested were found negative. 相似文献
175.
The relationship between ovarian steroids and uterine estrogen receptors during late pregnancy 总被引:1,自引:0,他引:1
Although a direct interdependence exists between the ovarian steroids, estrogen and progesterone, the exact role of these two hormones during pregnancy, especially late pregnancy, is not completely understood. Investigations have been conducted to determine whether the circulating levels of progesterone and estrogen or changes in the ratio of progesterone/estrogen in relation to the concentration of uterine estrogen receptors are associated with triggering parturition. Ninety-day old female rats were sacrificed at gestation days 14, 16, 18, 20 and two days post-partum. The plasma levels of estradiol and progesterone were measured by solid-phase radioimmunoassay. Uterine cytosol was subjected to a charcoal binding assay to determine the concentration of estrogen receptors. Our findings demonstrate that there is a significant (p less than 0.05) drop in both plasma progesterone and estradiol during late pregnancy. Also indicated is a significant (p less than 0.05) increase in uterine estrogen receptors throughout late pregnancy. Finally, during this period there is a direct correlation between the shift in the progesterone/estrogen ratio and the increase in the concentration of uterine estrogen receptors in late pregnancy. 相似文献
176.
Scrambled exons 总被引:23,自引:0,他引:23
J M Nigro K R Cho E R Fearon S E Kern J M Ruppert J D Oliner K W Kinzler B Vogelstein 《Cell》1991,64(3):607-613
177.
Molecular nature of Spemann's organizer: the role of the Xenopus homeobox gene goosecoid. 总被引:32,自引:0,他引:32
This study analyzes the function of the homeobox gene goosecoid in Xenopus development. First, we find that goosecoid mRNA distribution closely mimics the expected localization of organizer tissue in normal embryos as well as in those treated with LiCl and UV light. Second, goosecoid mRNA accumulation is induced by activin, even in the absence of protein synthesis. It is not affected by bFGF and is repressed by retinoic acid. Lastly, microinjection of goosecoid mRNA into the ventral side of Xenopus embryos, where goosecoid is normally absent, leads to the formation of an additional complete body axis, including head structures and abundant notochordal tissue. The results suggest that the goosecoid homeodomain protein plays a central role in executing Spemann's organizer phenomenon. 相似文献
178.
The anteroposterior character of mesoderm induced by a peptide growth factor (XTC-MIF) was tested by transplantation into host Xenopus gastrulae. Both retinoic acid and a homeodomain protein were able to override the anteriorizing effect of the growth factor. Microinjection of a posteriorly expressed homeobox mRNA can respecify anteroposterior identity, transforming head mesoderm into tail-inducing mesoderm. Unexpectedly, overexpression of XIHbox 6 protein in the transplanted cells, without addition of growth factors, caused the formation of tail-like structures. The cells overexpressing XIHbox 6 were able to recruit cells from the host into the secondary axis. The results suggest that vertebrate homeodomain proteins are part of the biochemical pathway leading to the generation of the body axis. 相似文献
179.
180.
Summary The production of somatic embryos from carrot suspension cultures invariably decreases through simple, repeated subculturing.
Extracellular, concentrated compounds extracted from already established embryo culture not only recovered the embryogenic
capability, but also accelerated the embryo production as much as two-fold (up to 1600 embryos/ml) compared with that of a
control culture. Sugars, which were only a small portion of the total concentrate, were excluded as possible causative factors.
It is likely that a protein fraction that is generated directly by competent, embryogenic cultures is important for the restoration
of embryogenic potential. 相似文献