全文获取类型
收费全文 | 2288篇 |
免费 | 177篇 |
专业分类
2465篇 |
出版年
2023年 | 20篇 |
2022年 | 20篇 |
2021年 | 49篇 |
2020年 | 38篇 |
2019年 | 54篇 |
2018年 | 42篇 |
2017年 | 36篇 |
2016年 | 71篇 |
2015年 | 102篇 |
2014年 | 106篇 |
2013年 | 122篇 |
2012年 | 189篇 |
2011年 | 178篇 |
2010年 | 88篇 |
2009年 | 101篇 |
2008年 | 133篇 |
2007年 | 127篇 |
2006年 | 113篇 |
2005年 | 100篇 |
2004年 | 105篇 |
2003年 | 106篇 |
2002年 | 106篇 |
2001年 | 35篇 |
2000年 | 16篇 |
1999年 | 38篇 |
1998年 | 27篇 |
1997年 | 19篇 |
1996年 | 15篇 |
1995年 | 21篇 |
1994年 | 13篇 |
1993年 | 10篇 |
1992年 | 18篇 |
1991年 | 24篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 16篇 |
1987年 | 22篇 |
1986年 | 14篇 |
1985年 | 16篇 |
1984年 | 10篇 |
1983年 | 12篇 |
1982年 | 9篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1971年 | 7篇 |
1969年 | 8篇 |
1965年 | 7篇 |
排序方式: 共有2465条查询结果,搜索用时 0 毫秒
131.
132.
This review summarizes our present knowledge about the composition and function of the plant nuclear envelope. Compared with animals or yeast, our molecular understanding of the nuclear envelope in higher plants is in its infancy. However, fundamental differences in the structure and function of the plant and animal nuclear envelope have already been found. Here, we compare and contrast these differences with respect to nuclear pore complexes, targeting of Ran signaling to the nuclear envelope, inner nuclear envelope proteins, and the role and fate of the nuclear envelope during mitosis. Further investigation of the emerging fundamental differences as well as the similarities between kingdoms might illuminate why there appears to be more than one blueprint for building a nucleus.Abbreviations
GFP
Green fluorescent protein
-
INE
Inner nuclear envelope
-
LAP
Lamina-associated polypeptide
-
LBR
Lamin B receptor
-
MTOC
Microtubule-organizing center
-
NE
Nuclear envelope
-
NPC
Nuclear pore complex
-
ONE
Outer nuclear envelope
-
RanBP
Ran-binding protein
-
RanGAP
Ran GTPase-activating protein
-
WPP domain
Tryptophan–proline–proline domain 相似文献
133.
Jafelice RM de Barros LC Bassanezi RC Gomide F 《Bulletin of mathematical biology》2004,66(6):1597-1620
This paper introduces a model for the evolution of positive HIV population and manifestation of AIDS (acquired immunideficiency
syndrome). The focus is on the nature of the transference rate of HIV to AIDS. Expert knowledge indicates that the transference
rate is uncertain and depends strongly on the viral load and the CD4+ level of the infected individuals. Here, we suggest to view the transference rate as a fuzzy set of the viral load and
CD4+ level values. In this case the dynamic model results in a fuzzy model that preserves the biological meaning and nature
of the transference rate λ. Its behavior fits the natural history of HIV infection reported in the medical science domain. The paper also includes a
comparison between the fuzzy model and a classic Anderson’s model using data reported in the literature. 相似文献
134.
Changes in plasma gonadotropin concentrations and urethral closure pressure in the bitch during the 12 months following ovariectomy 总被引:3,自引:0,他引:3
Reichler IM Pfeiffer E Piché CA Jöchle W Roos M Hubler M Arnold S 《Theriogenology》2004,62(8):1391-1402
Urinary incontinence due to acquired urethral sphincter incompetence is a common side effect of spaying, for which the underlying cause remains unknown. Spaying not only results in a significant reduction in the urethral closure pressure within 1 year but also in an increase in the plasma gonadotropin concentrations. To investigate the possible link between the post-ovariectomy changes in plasma gonadotropins and in urethral closure pressure, gonadotropin and urodynamic measurements were performed in 10 Beagle bitches before and for a period of 1 year after spaying. Plasma gonadotropin concentrations rose quickly after ovariectomy and peak levels were seen within 3-5 weeks, followed by a sharp drop until week 10. A steady increase was observed subsequently until week 42, when a plateau was reached. One year after spaying, the mean FSH concentration was 75.3 +/- 32.1 ng/ml, a 17-fold increase, and the LH was 8.3 +/- 3.8 ng/ml, an eightfold increase over the pre-spaying values. Ten months after spaying, the mean urethral closure pressure (9.7 cm H2O) was significantly reduced when compared to the mean pre-operative value of 15.4 cm H2O. However, there was no clear relationship between the gonadotropin concentrations and the urethral closure pressure. From these results it seems unlikely that chronically elevated gonadotropins are the underlying cause for reduced urethral closure pressure after spaying resulting in urinary incontinence. 相似文献
135.
Rapid and sensitive NMR method for osmolyte determination 总被引:4,自引:0,他引:4
We propose a rapid and sensitive method for osmolyte determination, based on one-dimensional and two-dimensional 1H NMR spectroscopy applied directly on culture of haloalkalophilic Halomonas pantelleriensis and acidothermophilic archaeon Sulfolobus solfataricus, without any extraction procedure. The osmoprotectants hydroxyectoine, ectoine, glutamate, glycine-betaine and treahalose can easily be quantified by integrating the peak areas with respect to an internal standard, and the concentrations evaluated with this method are in excellent agreement with the values previously reported. Furthermore, trace amount of osmoprotectants, often undetectable after extraction procedures, can also be evaluated. 相似文献
136.
137.
Ohren JF Chen H Pavlovsky A Whitehead C Zhang E Kuffa P Yan C McConnell P Spessard C Banotai C Mueller WT Delaney A Omer C Sebolt-Leopold J Dudley DT Leung IK Flamme C Warmus J Kaufman M Barrett S Tecle H Hasemann CA 《Nature structural & molecular biology》2004,11(12):1192-1197
MEK1 and MEK2 are closely related, dual-specificity tyrosine/threonine protein kinases found in the Ras/Raf/MEK/ERK mitogen-activated protein kinase (MAPK) signaling pathway. Approximately 30% of all human cancers have a constitutively activated MAPK pathway, and constitutive activation of MEK1 results in cellular transformation. Here we present the X-ray structures of human MEK1 and MEK2, each determined as a ternary complex with MgATP and an inhibitor to a resolution of 2.4 A and 3.2 A, respectively. The structures reveal that MEK1 and MEK2 each have a unique inhibitor-binding pocket adjacent to the MgATP-binding site. The presence of the potent inhibitor induces several conformational changes in the unphosphorylated MEK1 and MEK2 enzymes that lock them into a closed but catalytically inactive species. Thus, the structures reported here reveal a novel, noncompetitive mechanism for protein kinase inhibition. 相似文献
138.
Until now, the predominant use cases of industrial robots have been routine handling tasks in the automotive industry. In biotechnology and tissue engineering, in contrast, only very few tasks have been automated with robots. New developments in robot platform and robot sensor technology, however, make it possible to automate plants that largely depend on human interaction with the production process, e.g., for material and cell culture fluid handling, transportation, operation of equipment, and maintenance. In this paper we present a robot system that lends itself to automating routine tasks in biotechnology but also has the potential to automate other production facilities that are similar in process structure. After motivating the design goals, we describe the system and its operation, illustrate sample runs, and give an assessment of the advantages. We conclude this paper by giving an outlook on possible further developments. 相似文献
139.
Loredana R Barbara D Annamaria L Stefania T Maria MC Silvana F Piero A Marina P 《Molecular reproduction and development》2003,66(1):54-59
In the present paper we investigated the role played by apoptosis during oogenesis in the cartilaginous fish Torpedo marmorata. TEM, TUNEL and immunohistochemical techniques were employed to specifically reveal morphological and biochemical hallmarks of apoptosis in specimens from birth to sexual maturity. Data obtained demonstrate that apoptosis occurs in prefollicular oocyte selection, in maintaining the homeostasis of granulosa in healthy growing oocyte and in resorbing atretic follicles. In this respect, the involvement of apoptosis in Torpedo marmorata oogenesis closely parallels that found in mammals, thus confirming that strategies of germ cell selection among vertebrates have been evolutionarily preserved. 相似文献
140.
Jonkers IJ Smelt AH Hattori H Scheek LM van Gent T de Man FH van der Laarse A van Tol A 《Journal of lipid research》2003,44(8):1462-1469
Hypertriglyceridemia (HTG) is associated with insulin resistance, increased cholesteryl ester transfer (CET), and low HDL cholesterol. Phospholipid transfer protein (PLTP) may be involved in these relationships. Associations between CET, lipids, insulin resistance, CETP and PLTP activities, and PLTP mass were investigated in 18 HTG patients and 20 controls. Effects of 6 weeks of bezafibrate treatment were studied in HTG patients. HTG patients had higher serum triglycerides, insulin resistance, free fatty acid (FFA), and CET, lower levels of HDL cholesterol (-44%) and PLTP mass (-54%), and higher CETP (+20%) and PLTP activity (+48%) than controls. Bezafibrate reduced triglycerides, CET (-37%), insulin resistance (-53%), FFA (-48%), CETP activity (-12%), PLTP activity (-8%), and increased HDL cholesterol (+27%), whereas PLTP mass remained unchanged. Regression analysis showed a positive contribution of PLTP mass (P = 0.001) but not of PLTP activity to HDL cholesterol, whereas insulin resistance positively contributed to PLTP activity (P < 0.01). Bezafibrate-induced change in CET and HDL cholesterol correlated with changes in CETP activity and FFAs, but not with change in PLTP activity. Bezafibrate-induced change in PLTP activity correlated with change in FFAs (r = 0.455, P = 0.058). We propose that elevated PLTP activity in HTG is related to insulin resistance and not to increased PLTP mass. Bezafibrate-induced diminished insulin resistance is associated with a reduction of CET and PLTP activity. 相似文献