全文获取类型
收费全文 | 1075篇 |
免费 | 116篇 |
出版年
2022年 | 9篇 |
2021年 | 12篇 |
2020年 | 12篇 |
2019年 | 12篇 |
2018年 | 19篇 |
2017年 | 16篇 |
2016年 | 27篇 |
2015年 | 27篇 |
2014年 | 39篇 |
2013年 | 71篇 |
2012年 | 48篇 |
2011年 | 66篇 |
2010年 | 48篇 |
2009年 | 42篇 |
2008年 | 55篇 |
2007年 | 50篇 |
2006年 | 58篇 |
2005年 | 60篇 |
2004年 | 60篇 |
2003年 | 50篇 |
2002年 | 46篇 |
2001年 | 10篇 |
2000年 | 16篇 |
1999年 | 12篇 |
1998年 | 8篇 |
1997年 | 12篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1993年 | 9篇 |
1992年 | 16篇 |
1991年 | 14篇 |
1990年 | 9篇 |
1989年 | 16篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 15篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1980年 | 8篇 |
1979年 | 19篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1975年 | 6篇 |
1974年 | 9篇 |
1973年 | 12篇 |
1972年 | 12篇 |
1970年 | 7篇 |
1969年 | 7篇 |
1968年 | 6篇 |
排序方式: 共有1191条查询结果,搜索用时 78 毫秒
91.
Grzelak K Kłdkiewicz B Kolomiets LI Debski J Dadlez M Lalik A Ozyhar A Kochman M 《Protein expression and purification》2003,31(2):173-180
Galleria mellonella juvenile hormone binding protein (JHBP) is a single chain glycoprotein with two disulfide bonds and a molecular mass of 25,880 Da. This report describes the expression of JHBP in bacteria and yeast cells (Pichia pastoris). The expression in bacteria was low and the protein was rapidly degraded upon cell lysis. The expression of His8-tagged rJHBP (His8-rJHBP) in P. pastoris was high and the non-degraded protein was purified to homogeneity with high yield in a one-step immobilized Ni++ affinity chromatography. His8-rJHBP from P. pastoris contains one JH III binding site with KD of 3.7 +/- 1.3x10(-7) M. The results suggest that P. pastoris is the preferred system for expression of His8-rJHBP in non-degraded fully active form. 相似文献
92.
Karasek M Stankiewicz A Bandurska-Stankiewicz E Zylinska K Pawlikowski M Kuzdak K 《Neuro endocrinology letters》2000,21(6):437-439
OBJECTIVES: Surgical removal of a very large goiter may traumatize adjacent anatomical structures. The manipulations that involve superior cervical ganglia may alter melatonin secretion. To test this hypothesis we decided to study diurnal serum melatonin profiles in patients with a very large goiter before and after the surgery. MATERIAL AND METHODS:The study was performed on 10 women (mean age-46.5+/-1.6 years; mean+/-SEM; range 39-54 years) with very large non-toxic nodular goiter (mean thyroid volume-125.8+/-25.9 cm (3); mean+/-SEM; range 82.6-326.7 cm(3)). Diurnal serum melatonin profiles were estimated two days before the operation and 10 days after the surgery. Blood samples were collected at 08:00, 12:00, 16:00, 20:00, 22:00, 24:00, 02:00, 04:00, 06:00 and 08:00 h. Melatonin concentration was measured using RIA kit. RESULTS: Nocturnal serum melatonin concentrations (at 24, 02, and 04 hours) were significantly higher after the surgery than before the operation. CONCLUSIONS: Very large goiter may compress the superior cervical ganglia altering indirectly the melatonin synthesis. It cannot be excluded, however, that the presence of the large goiter in some other way affects melatonin secretion. 相似文献
93.
Smith E Redman RA Logg CR Coetzee GA Kasahara N Frenkel B 《The Journal of biological chemistry》2000,275(26):19992-20001
Unique cell cycle control is instituted in confluent osteoblast cultures, driving growth to high density. The postconfluent dividing cells share features with cells that normally exit the cell cycle; p27(kip1) is increased, p21(waf1/cip1) is decreased, free E2F DNA binding activity is reduced, and E2F4 is primarily nuclear. E2F4-p130 becomes the predominant E2F-pocket complex formed on E2F sites, but, unlike the complex that typifies resting cells, cyclin A and CDK2 are also present. Administration of dexamethasone at this, but not earlier stages, results in reduction of cyclin A and CDK2 levels with a parallel decrease in the associated kinase activity, dissociation of cyclin A-CDK2 from the E2F4-p130 complexes, and inhibition of G(1)/S transition. The glucocorticoid-mediated cell cycle attenuation is also accompanied by, but not attributable to, increased p27(kip1) and decreased p21(waf1/cip1) levels. The attenuation of osteoblast growth to high density by dexamethasone is associated with severe impairment of mineralized extracellular matrix formation, unless treatment commences in cultures that have already grown to high density. Both the antimitotic and the antiphenotypic effects are reversible, and both are antagonized by RU486. Thus, glucocorticoids induce premature attenuation of the osteoblast cell cycle, possibly contributing to the osteoporosis induced by these drugs in vivo. 相似文献
94.
95.
Egg cells were analysed cytologically during the female receptivity period in maize (Zea mays L., line A 188). Three classes of egg cell were distinguished: type A – small, non-vacuolated cells with a central nucleus;
type B – larger cells with small vacuoles surrounding the perinuclear cytoplasm located in the middle of the cell; type C
– big cells with a large apical vacuole and the mid-basal perinuclear cytoplasm. The less-dense cytoplasm of the vacuolated
egg cells usually contained numerous cup- or bell-shaped mitochondria. The three egg types appear to correspond to three late
stages of egg cell differentiation. The frequencies of each of the three egg types were monitored in developing maize ears
before and after pollination. In young ears, with the silks just extending out of the husks, small A-type cells were found
in about 86% of ovules. Their frequency decreased to about 58% at the optimum silk length, remained unchanged in non-pollinated
ears, and fell to 16% at the end of the female receptivity period. However, after pollination and before fertilisation the
frequency of these cells decreased to about 33%, and the larger vacuolated egg cells (types B and C) prevailed. At various
stages of the receptivity period, pollination accelerated changes in the egg population, increasing the number of ovules bearing
larger, vacuolated egg cells. Experiments with silk removal demonstrated that putative pollination signals act immediately
after pollen deposition and are not species-specific.
Received: 5 February 1999 / Accepted: 28 August 1999 相似文献
96.
Although it is known that drug addicts are a high-risk group for disruption of many homeostatic processes, little is know
about changes in serum trace elements concentrations after taking the psychoactive substances. The aim of the study was to
check the influence of the taking homemade heroin on serum level of copper. Blood samples were taken from 30 opiate addicts,
and copper concentrations were measured by the means of atomic absorption spectrophotometry. The result of the study show
that in the examined group, copper serum concentrations (1.35 mg/L) upon admission to the clinic were higher than in the control
group (1.11 mg/L) but decreased during hospitalization (1.18 mg/L). There was no correlation between duration of stay at the
hospital and changes in serum copper concentration. 相似文献
97.
Seed Rain in Natural Grassland and Adjacent Ski Run in the Swiss Alps: A Preliminary Report 总被引:1,自引:0,他引:1
Seed rain was studied during one growing season in an intact high-alpine grassland and in a downhill ski run that had been machine-graded about 26 years earlier. The study plots were located at about 2500 meters above sea level. The number of trapped seeds per square meter in the grassland was significantly larger than in the ski run (930 versus 96, respectively). Alpha diversity in seed rain was about two times higher in the grassland than in the ski run. Seed rain was primarily influenced by site conditions but also varied in space and time, and both the actual number of diaspores and the species composition changed throughout the growing season. Most of the species found in the seed rain occurred in the standing vegetation, but some clearly arrived from outside. Seed rain in both sites was dominated by a few species, and no clear relationships were found between the species abundance in standing vegetation and in the seed rain. The results of this preliminary study contribute to a better understanding of plant behavior in high-alpine sites and will be helpful in planning and implementing restoration work above the timberline. 相似文献
98.
Exposure of A2780 human ovarian tumor cells to a low concentration of melphalan in vitro for 7 d results in the development of melphalan resistance, which is dependent on elevated cellular levels of glutathione and glutathioneS-transferase. The inclusion of selenite (at concentrations as low as 0.2 ΜM) during the exposure to melphalan completely prevented the development of resistance. Selenite did not prevent the melphalan-induced increase in glutathione, but it did prevent the increase in the activity of glutathioneS-transferase. It also prevented the increase in the expression of the glutathioneS-transferase gene, suggesting that this may be the mechanism by which it prevents the development of melphalan resistance. The results of this in vitro study suggest that selenite may prove to be useful in preventing the development of drug resistance in vivo. 相似文献
99.
Marta Winiecka-Klimek Maciej Smolarz Maciej P. Walczak Jolanta Zieba Krystyna Hulas-Bigoszewska Blazej Kmieciak Sylwester Piaskowski Piotr Rieske Dawid P. Grzela Ewelina Stoczynska-Fidelus 《PloS one》2015,10(11)
Tumorigenic potential of induced pluripotent stem cells (iPSCs) infiltrating population of induced neural stem cells (iNSCs) generated from iPSCs may limit their medical applications. To overcome such a difficulty, direct reprogramming of adult somatic cells into iNSCs was proposed. The aim of this study was the systematic comparison of induced neural cells (iNc) obtained with different methods—direct reprogramming of human adult fibroblasts with either SOX2 (SiNSc-like) or SOX2 and c-MYC (SMiNSc-like) and induced pluripotent stem cells differentiation to ebiNSc—in terms of gene expression profile, differentiation potential as well as proliferation properties. Immunocytochemistry and real-time PCR analyses were used to evaluate gene expression profile and differentiation potential of various iNc types. Bromodeoxyuridine (BrdU) incorporation and senescence-associated beta-galactosidase (SA-β-gal) assays were used to estimate proliferation potential. All three types of iNc were capable of neuronal differentiation; however, astrocytic differentiation was possible only in case of ebiNSc. Contrary to ebiNSc generation, the direct reprogramming was rarely a propitious process, despite 100% transduction efficiency. The potency of direct iNSCs-like cells generation was lower as compared to iNSCs obtained by iPSCs differentiation, and only slightly improved when c-MYC was added. Directly reprogrammed iNSCs-like cells were lacking the ability to differentiate into astrocytic cells and characterized by poor efficiency of neuronal cells formation. Such features indicated that these cells could not be fully reprogrammed, as confirmed mainly with senescence detection. Importantly, SiNSc-like and SMiNSc-like cells were unable to achieve the long-term survival and became senescent, which limits their possible therapeutic applicability. Our results suggest that iNSCs-like cells, generated in the direct reprogramming attempts, were either not fully reprogrammed or reprogrammed only into neuronal progenitors, mainly because of the inaccuracies of currently available protocols. 相似文献
100.
Simona Littnerova Petr Kala Jiri Jarkovsky Lenka Kubkova Krystyna Prymusova Petr Kubena Martin Tesak Ondrej Toman Martin Poloczek Jindrich Spinar Ladislav Dusek Jiri Parenica 《PloS one》2015,10(4)