全文获取类型
收费全文 | 2724篇 |
免费 | 168篇 |
国内免费 | 159篇 |
出版年
2023年 | 46篇 |
2022年 | 39篇 |
2021年 | 54篇 |
2020年 | 73篇 |
2019年 | 75篇 |
2018年 | 71篇 |
2017年 | 50篇 |
2016年 | 74篇 |
2015年 | 76篇 |
2014年 | 99篇 |
2013年 | 177篇 |
2012年 | 97篇 |
2011年 | 141篇 |
2010年 | 85篇 |
2009年 | 111篇 |
2008年 | 128篇 |
2007年 | 145篇 |
2006年 | 139篇 |
2005年 | 117篇 |
2004年 | 111篇 |
2003年 | 95篇 |
2002年 | 99篇 |
2001年 | 75篇 |
2000年 | 61篇 |
1999年 | 52篇 |
1998年 | 53篇 |
1997年 | 64篇 |
1996年 | 49篇 |
1995年 | 32篇 |
1994年 | 58篇 |
1993年 | 50篇 |
1992年 | 33篇 |
1991年 | 39篇 |
1990年 | 30篇 |
1989年 | 19篇 |
1988年 | 21篇 |
1987年 | 26篇 |
1986年 | 11篇 |
1985年 | 30篇 |
1984年 | 42篇 |
1983年 | 29篇 |
1982年 | 19篇 |
1981年 | 31篇 |
1980年 | 19篇 |
1979年 | 20篇 |
1978年 | 19篇 |
1977年 | 23篇 |
1976年 | 14篇 |
1975年 | 13篇 |
1973年 | 6篇 |
排序方式: 共有3051条查询结果,搜索用时 598 毫秒
921.
After the initial discovery of intermediate filament (IF)–forming proteins in 1968, a decade would elapse before they were revealed to comprise a diverse group of proteins which undergo tissue-, developmental stage-, differentiation-, and context-dependent regulation. Our appreciation for just how large (n = 70), conserved, complex, and dynamic IF genes and proteins are became even sharper upon completion of the human genome project. While there has been extraordinary progress in understanding the multimodal roles of IFs in cells and tissues, even revealing them as direct causative agents in a broad array of human genetic disorders, the link between individual IFs and cell differentiation has remained elusive. Here, we review evidence that demonstrates a role for IFs in lineage determination, cell differentiation, and tissue homeostasis. A major theme in this review is the function of IFs as sensors and transducers of mechanical forces, intersecting microenvironmental cues and fundamental processes through cellular redox balance. 相似文献
922.
923.
栀子花氨基酸成分的分析测定 总被引:1,自引:0,他引:1
目的:研究栀子花中氨基酸成分的种类及含量,为栀子花的开发利用提供科学依据.方法:将栀子花粉末用盐酸恒温水解处理,水解液用氨基酸自动分析仪测定.结果:栀子花含有17种氨基酸,其中7种人体必需氨基酸的质量分数达26.7mg·g-1,占总量的36.6%.结论:栀子花中氨基酸质量分数达7.3%,是一种很有开发价值的药食两用植物... 相似文献
924.
首次采用高效液相色谱法对中药复方止咳清肺胶囊中的有效成分—芥子碱硫氰酸盐进行了含量测定研究,由此建立了该复方的HPLC法质量分析方法。 相似文献
925.
926.
Selection is expected to maintain primary sex ratios at an evolutionary equilibrium. In organisms with temperature-dependent sex determination (TSD), targets of sex-ratio selection include the thermal sensitivity of the sex-determining pathway (hereafter, sex determination threshold) and nest-site choice. However, offspring sex may be canalized for nests located in thermally extreme environments; thus, genetic variance for the sex determination threshold is not expressed and is invisible to direct selection. The concept of 'effective heritability' accounts for this dependence and provides a more realistic prediction of the expected evolutionary response to selection in the wild. Past estimates of effective heritability of the sex determination threshold, which were derived from laboratory data, suggested that the potential for the sex determination threshold to evolve in the wild was extremely low. We re-evaluated original estimates of this parameter by analysing field-collected measures of nest temperatures, vegetation cover and clutch sex ratios from nests in a population of painted turtles (Chrysemys picta). We coupled these data with measurements of broad-sense heritability of the sex determination threshold in C. picta, using an experiment that splits clutches of eggs between a constant temperature (i.e. typical laboratory incubation) and a daily fluctuating temperature (i.e. similar to natural nests) with the same mean. We found that (i) the effective heritability of the sex determination threshold appears to have been historically underestimated and the effective heritability of nest-site choice has been overestimated and (ii) significant family-by-incubation treatment interaction exists for sex for C. picta between constant- and fluctuating-temperature regimes. Our results suggest that the thermal sensitivity of the sex-determining pathway may play a larger, more complex role in the microevolution of TSD than traditionally thought. 相似文献
927.
The SRY (sex-determining region on the Y chromosome) is essential for male development; however, the molecular mechanism by which the SRY induces testis development is still unclear. To elucidate the mechanism of testis development, we identified SRY-interacting proteins using a yeast two-hybrid system. We found two ribosomal proteins, RPS7 (ribosomal protein S7) and RPL13a (ribosomal protein L13a) that interact with the HMG (high-mobility group) box domain of SRY. Furthermore, we confirmed the intracellular distributions of RPS7, RPL13a and SRY and found that the three proteins were co-expressed in COS1 cells. SRY, RPS7 and RPL13a were co-localized in nuclear speckles. These findings suggest that SRY plays an important role in activities associated with nuclear speckles via an unknown mechanism. 相似文献
928.
In this paper, a simple and novel method for the determination of polychlorinated biphenyls (PCBs), using silver nanoparticles (AgNPs) as a resonance light scattering (RLS) probe, is proposed. Under optimized conditions, there existed linear relationships between the enhancing RLS intensity of the system and the concentrations of PCBs in the range 8.0 × 10?8?1.0 × 10?6 g mL?1 for 2,4,4′‐trichlorbiphenyl (PCB28), 9.0 × 10?8?1.0 × 10?6 g mL?1 for 2,2′,5,5′‐tetrachlorbiphenyl (PCB52) and 4.0 × 10?8?1.0 × 10?6 g mL?1 for 3,3′,4,4′‐tetrachlorobiphenyl (PCB77). The corresponding detection limits (S/N = 3) were 2.6 × 10?8 g mL?1 for PCB28, 3.3 × 10?8 g mL?1 for PCB52 and 6.3 × 10?9 g mL?1 for PCB77, respectively. Finally, the mechanism of RLS enhancement was also studied. The results indicated that PCBs were adsorbed on the surface of AgNPs to form larger AgNP–PCB aggregates, resulting in the RLS enhancement of the system. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
929.
Based on the fluorescence quenching of Terbium (III)‐sodium hexametaphosphate (Tb/SHMP) chelates in the presence chromate (III), a sensitive fluorimetric method was developed for the determination of trace amounts of chromium (III) in aqueous solutions. Under the optimum conditions, the linear calibration graph was obtained (R = 0.996). The linear range and detection limit of Cr (III) were 7.69 × 10?7 to 1.15 × 10?4 mol L?1 and 4.50 × 10?7 mol L?1, respectively. The proposed method had a wider linear range and was proved to be very sensitive, rapid and simple. The method was applied successfully to the determination of chromium (III) in the synthetic samples and real water samples. Moreover, the reaction mechanism was discussed through the fluorescence lifetime and proved to be dynamic quenching behavior. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
930.
首次采用HPLC示差折光法测定藻油中DHA的含量。色谱柱为Eclipse XDB-C18(Analytical 4.6×250mm,5μm),流动相为乙腈∶四氢呋喃∶水(含0.4%HAC)=77∶3∶20,柱温为30℃,流速为1.0 mL/min。该条件下DHA在0.259~6.225 mg/mL内呈良好的线性关系,相关系数R2=0.9995,平均回收率为101.15%,RSD为1.98%(n=6)。该方法可靠、简便、重现性好,可作为藻油中DHA的定量方法。 相似文献